Lidar system

ABSTRACT

A lidar system with a light source to emit a pulse of light into a field of view and a receiver to detect a return pulse of light which is reflected or scattered by a target in the field of view. The receiver may include an avalanche photodiode to generate an electrical-current pulse corresponding to the return pulse and a transimpedance amplifier to produce a voltage pulse that corresponds to the electrical-current pulse. A voltage amplifier may amplify the voltage pulse and a comparator may produce an edge signal when the amplified voltage pulse exceeds a threshold. A time-to-digital converter may determine a time interval based on an emission time of the pulse of light and based on the edge signal. A processor may determine a distance to the target using the time interval.

INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS

Any and all applications for which a foreign or domestic priority claimis identified in the Application Data Sheet as filed with the presentapplication are hereby incorporated by reference under 37 CFR 1.57.Namely, this application is a continuation of U.S. patent applicationSer. No. 15/364,085, filed Nov. 29, 2016, and entitled “LIDAR SYSTEM,”which claims the benefit, under 35 U.S.C. §119(e), of U.S. ProvisionalPatent Application 62/261,214, filed Nov. 30, 2015, the entirety of eachof which is incorporated herein by reference.

BACKGROUND

Field

This disclosure generally relates to lidar systems.

Description of the Related Art

Light detection and ranging (lidar) is a technology that can be used tomeasure distances to remote targets. Typically, a lidar system includesa light source and a detector. The light source can be, for example, alaser which emits light having a particular operating wavelength. Theoperating wavelength of a lidar system may lie, for example, in theinfrared, visible, or ultraviolet portions of the electromagneticspectrum. The light source emits light toward a target which thenscatters the light. Some of the scattered light is received back at thedetector. The system determines the distance to the target based on oneor more characteristics associated with the returned light. For example,the system may determine the distance to the target based on the time offlight of a returned light pulse.

SUMMARY

In some embodiments, a lidar system comprises: a light source configuredto emit pulses of light; a scanner configured to scan at least a portionof the emitted pulses of light across a field of regard; and a receiverconfigured to detect at least a portion of the scanned pulses of lightscattered by a target located a distance from the lidar system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example light detection and ranging (lidar)system.

FIG. 2 illustrates an example scan pattern produced by a lidar system.

FIG. 3 illustrates an example lidar system that includes a laser,sensor, and laser-sensor link.

FIG. 4 illustrates an example lidar system where the laser-sensor linkincludes an optical link and an electrical link coupled between thelaser and sensor.

FIG. 5 illustrates an example lidar system with a laser coupled tomultiple sensor heads by multiple respective laser-sensor links.

FIG. 6 illustrates an example vehicle with a lidar system that includesa laser with multiple sensor heads coupled to the laser by multiplelaser-sensor links.

FIG. 7 illustrates an example laser with a seed laser and ademultiplexer that distributes light from the seed laser to multipleoptical links.

FIG. 8 illustrates an example seed laser that includes a laser diodedriven by a pulse generator.

FIG. 9 illustrates an example seed laser that includes a laser diode andan optical modulator.

FIG. 10 illustrates an example seed laser that includes a laser diodedriven by a pulse generator and an optical modulator driven by anotherpulse generator.

FIG. 11 illustrates an example seed laser with multiple laser diodesthat are combined together by a multiplexer.

FIG. 12 illustrates an example wavelength-dependent delay line.

FIG. 13 illustrates an example lidar system that includes a seed laser,amplifier, and sensor.

FIG. 14 illustrates an example spectrum of an optical signal before andafter passing through a spectral filter.

FIG. 15 illustrates example optical pulses before and after the pulsespass through a temporal filter.

FIG. 16 illustrates an example double-pass fiber-optic amplifier.

FIG. 17 illustrates example absorption spectra for erbium and ytterbiumions incorporated into a glass host (e.g., fused silica).

FIG. 18 illustrates example absorption and emission spectra for a glasshost doped with a combination of erbium and ytterbium.

FIG. 19 illustrates an example single-pass fiber-optic amplifier.

FIG. 20 illustrates an example booster amplifier that produces afree-space output beam.

FIG. 21 illustrates an example lidar system that includes threeamplifiers.

FIG. 22 illustrates an example lidar system with a laser that includes aseed laser and an amplifier.

FIG. 23 illustrates an example lidar system with an optical link thatincludes an amplifier.

FIG. 24 illustrates an example lidar system with a sensor head thatincludes an amplifier.

FIG. 25 illustrates an example lidar system where the sensor headincludes an amplifier coupled to an output collimator.

FIG. 26 illustrates an example lidar system where the sensor headincludes a free-space amplifier.

FIG. 27 illustrates an example laser where the seed laser is combinedwith a supplemental light source.

FIG. 28 illustrates an example laser that includes a seed laser,amplifier, and demultiplexer.

FIG. 29 illustrates an example laser that includes multiple laserdiodes, a multiplexer, an amplifier, and a demultiplexer.

FIG. 30 illustrates an example laser where the laser is coupled tomultiple optical links that each include an amplifier.

FIG. 31 illustrates an example laser with multiple laser diodes coupledto multiple respective optical links that each include an amplifier.

FIG. 32 illustrates an example lidar system with an example overlapmirror.

FIG. 33 illustrates an example light-source field of view and receiverfield of view for a lidar system.

FIG. 34 illustrates an example light-source field of view and receiverfield of view with a corresponding scan direction.

FIG. 35 illustrates an example receiver field of view that is offsetfrom a light-source field of view.

FIG. 36 illustrates an example forward-scan direction and reverse-scandirection for a light-source field of view and a receiver field of view.

FIG. 37 illustrates an example InGaAs avalanche photodiode (APD).

FIG. 38 illustrates an APD coupled to an example pulse-detectioncircuit.

FIG. 39 illustrates an APD coupled to an example multi-channelpulse-detection circuit.

FIG. 40 illustrates an example receiver that includes two APDs coupledto a logic circuit.

FIG. 41 illustrates an example detector array.

FIG. 42 illustrates an example computer system.

DETAILED DESCRIPTION

FIG. 1 illustrates an example light detection and ranging (lidar) system100. In particular embodiments, a lidar system 100 may be referred to asa laser ranging system, a laser radar system, a LIDAR system, or a laserdetection and ranging (LADAR or ladar) system. In particularembodiments, a lidar system 100 may include a light source 110, mirror115, scanner 120, receiver 140, or controller 150. The light source 110may be, for example, a laser which emits light having a particularoperating wavelength in the infrared, visible, or ultraviolet portionsof the electromagnetic spectrum. As an example, light source 110 mayinclude a laser with an operating wavelength between approximately 1.2μm and 1.7 μm. The light source 110 emits an output beam of light 125which may be continuous-wave, pulsed, or modulated in any suitablemanner for a given application. The output beam of light 125 is directeddownrange toward a remote target 130. As an example, the remote target130 may be located a distance D of approximately 1 m to 1 km from thelidar system 100.

Once the output beam 125 reaches the downrange target 130, the targetmay scatter or reflect at least a portion of light from the output beam125, and some of the scattered or reflected light may return toward thelidar system 100. In the example of FIG. 1, the scattered or reflectedlight is represented by input beam 135, which passes through scanner 120and is directed by mirror 115 to receiver 140. In particularembodiments, a relatively small fraction of the light from output beam125 may return to the lidar system 100 as input beam 135. As an example,the ratio of input beam 135 average power, peak power, or pulse energyto output beam 125 average power, peak power, or pulse energy may beapproximately 10⁻¹, 10⁻², 10⁻³, 10⁻⁴, 10⁻⁵, 10⁻⁶, 10⁻⁷, 10⁻⁸, 10⁻⁹,10⁻¹⁰, 10⁻¹¹, or 10⁻¹². As another example, if a pulse of output beam125 has a pulse energy of 1 microjoule (μJ), then the pulse energy of acorresponding pulse of input beam 135 may have a pulse energy ofapproximately 10 nanojoules (nJ), 1 nJ, 100 picojoules (pJ), 10 pJ, 1pJ, 100 femtojoules (fJ), 10 fJ, 1 fJ, 100 attojoules (aJ), 10 aJ, or 1aJ. In particular embodiments, output beam 125 may be referred to as alaser beam, light beam, optical beam, emitted beam, or beam. Inparticular embodiments, input beam 135 may be referred to as a returnbeam, received beam, return light, received light, input light,scattered light, or reflected light. As used herein, scattered light mayrefer to light that is scattered or reflected by a target 130. As anexample, an input beam 135 may include: light from the output beam 125that is scattered by target 130; light from the output beam 125 that isreflected by target 130; or a combination of scattered and reflectedlight from target 130.

In particular embodiments, receiver 140 may receive or detect photonsfrom input beam 135 and generate one or more representative signals. Forexample, the receiver 140 may generate an output electrical signal 145that is representative of the input beam 135. This electrical signal 145may be sent to controller 150. In particular embodiments, controller 150may include a processor, computing system (e.g., an ASIC or FPGA), orother suitable circuitry configured to analyze one or morecharacteristics of the electrical signal 145 from the receiver 140 todetermine one or more characteristics of the target 130, such as itsdistance downrange from the lidar system 100. This can be done, forexample, by analyzing the time of flight or phase modulation for a beamof light 125 transmitted by the light source 110. If lidar system 100measures a time of flight of T (e.g., T represents the round-trip timefor light to travel from the lidar system 100 to the target 130 and backto the lidar system 100), then the distance D from the target 130 to thelidar system 100 may be expressed as D=c·T/2, where c is the speed oflight (approximately 3.0×10⁸ m/s). As an example, if a time of flight ismeasured to be T=300 ns, then the distance from the target 130 to thelidar system 100 may be determined to be approximately D=45.0 m. Asanother example, if a time of flight is measured to be T=1.33 μs, thenthe distance from the target 130 to the lidar system 100 may bedetermined to be approximately D=199.5 m. In particular embodiments, adistance D from lidar system 100 to a target 130 may be referred to as adistance, depth, or range of target 130. As used herein, the speed oflight c refers to the speed of light in any suitable medium, such as forexample in air, water, or vacuum. As an example, the speed of light invacuum is approximately 2.9979×10⁸ m/s, and the speed of light in air(which has a refractive index of approximately 1.0003) is approximately2.9970×10⁸ m/s.

In particular embodiments, light source 110 may include a pulsed laser.As an example, light source 110 may be a pulsed laser that producespulses of light with a pulse duration or pulse width of approximately 10picoseconds (ps) to 20 nanoseconds (ns). As another example, lightsource 110 may be a pulsed laser that produces pulses with a pulseduration of approximately 200-400 ps. As another example, light source110 may be a pulsed laser that produces pulses at a pulse repetitionfrequency of approximately 100 kHz to 5 MHz or a pulse period (e.g., atime between consecutive pulses) of approximately 200 ns to 10 μs. Inparticular embodiments, light source 110 may have a substantiallyconstant pulse repetition frequency, or light source 110 may have avariable or adjustable pulse repetition frequency. As an example, lightsource 110 may be a pulsed laser that produces pulses at a substantiallyconstant pulse repetition frequency of approximately 640 kHz (e.g.,640,000 pulses per second), corresponding to a pulse period ofapproximately 1.56 μs. As another example, light source 110 may have apulse repetition frequency that can be varied from approximately 700 kHzto 3 MHz.

In particular embodiments, light source 110 may produce a free-spaceoutput beam 125 having any suitable average optical power, and theoutput beam 125 may have optical pulses with any suitable pulse energyor peak optical power. As an example, output beam 125 may have anaverage power of approximately 1 mW, 10 mW, 100 mW, 1 W, 10 W, or anyother suitable average power. As another example, output beam 125 mayinclude pulses with a pulse energy of approximately 0.1 μJ, 1 μJ, 10 μJ,100 μJ, 1 mJ, or any other suitable pulse energy. As another example,output beam 125 may include pulses with a peak power of approximately 10W, 100 W, 1 kW, 5 kW, 10 kW, or any other suitable peak power. Anoptical pulse with a duration of 400 ps and a pulse energy of 1 μJ has apeak power of approximately 2.5 kW. If the pulse repetition frequency is500 kHz, then the average power of an output beam 125 with 1-μJ pulsesis approximately 0.5 W.

In particular embodiments, light source 110 may include a laser diode,such as for example, a Fabry-Perot laser diode, a quantum well laser, adistributed Bragg reflector (DBR) laser, a distributed feedback (DFB)laser, or a vertical-cavity surface-emitting laser (VCSEL). As anexample, light source 110 may include an aluminum-gallium-arsenide(AlGaAs) laser diode, an indium-gallium-arsenide (InGaAs) laser diode,or an indium-gallium-arsenide-phosphide (InGaAsP) laser diode. Inparticular embodiments, light source 110 may include a pulsed laserdiode with a peak emission wavelength of approximately 1400-1600 nm. Asan example, light source 110 may include a laser diode that is currentmodulated to produce optical pulses. In particular embodiments, lightsource 110 may include a pulsed laser diode followed by one or moreoptical-amplification stages. As an example, light source 110 may be afiber-laser module that includes a current-modulated laser diode with apeak wavelength of approximately 1550 nm followed by a single-stage or amulti-stage erbium-doped fiber amplifier (EDFA). As another example,light source 110 may include a continuous-wave (CW) or quasi-CW laserdiode followed by an external optical modulator (e.g., an electro-opticmodulator), and the output of the modulator may be fed into an opticalamplifier.

In particular embodiments, an output beam of light 125 emitted by lightsource 110 may be a collimated optical beam with any suitable beamdivergence, such as for example, a divergence of approximately 0.1 to3.0 milliradian (mrad). A divergence of output beam 125 may refer to anangular measure of an increase in beam size (e.g., a beam radius or beamdiameter) as output beam 125 travels away from light source 110 or lidarsystem 100. In particular embodiments, output beam 125 may have asubstantially circular cross section with a beam divergencecharacterized by a single divergence value. As an example, an outputbeam 125 with a circular cross section and a divergence of 1 mrad mayhave a beam diameter or spot size of approximately 10 cm at a distanceof 100 m from lidar system 100. In particular embodiments, output beam125 may be an astigmatic beam or may have a substantially ellipticalcross section and may be characterized by two divergence values. As anexample, output beam 125 may have a fast axis and a slow axis, where thefast-axis divergence is greater than the slow-axis divergence. Asanother example, output beam 125 may be an astigmatic beam with afast-axis divergence of 2 mrad and a slow-axis divergence of 0.5 mrad.

In particular embodiments, an output beam of light 125 emitted by lightsource 110 may be unpolarized or randomly polarized, may have nospecific or fixed polarization (e.g., the polarization may vary withtime), or may have a particular polarization (e.g., output beam 125 maybe linearly polarized, elliptically polarized, or circularly polarized).As an example, light source 110 may produce linearly polarized light,and lidar system 100 may include a quarter-wave plate that converts thislinearly polarized light into circularly polarized light. The circularlypolarized light may be transmitted as output beam 125, and lidar system100 may receive input beam 135, which may be substantially or at leastpartially circularly polarized in the same manner as the output beam 125(e.g., if output beam 125 is right-hand circularly polarized, then inputbeam 135 may also be right-hand circularly polarized). The input beam135 may pass through the same quarter-wave plate (or a differentquarter-wave plate) resulting in the input beam 135 being converted tolinearly polarized light which is orthogonally polarized (e.g.,polarized at a right angle) with respect to the linearly polarized lightproduced by light source 110. As another example, lidar system 100 mayemploy polarization-diversity detection where two polarizationcomponents are detected separately. The output beam 125 may be linearlypolarized, and the lidar system 100 may split the input beam 135 intotwo polarization components (e.g., s-polarization and p-polarization)which are detected separately by two photodiodes (e.g., a balancedphotoreceiver that includes two photodiodes).

In particular embodiments, lidar system 100 may include one or moreoptical components configured to condition, shape, filter, modify,steer, or direct the output beam 125 or the input beam 135. As anexample, lidar system 100 may include one or more lenses, mirrors,filters (e.g., bandpass or interference filters), beam splitters,polarizers, polarizing beam splitters, wave plates (e.g., half-wave orquarter-wave plates), diffractive elements, or holographic elements. Inparticular embodiments, lidar system 100 may include a telescope, one ormore lenses, or one or more mirrors to expand, focus, or collimate theoutput beam 125 to a desired beam diameter or divergence. As an example,the lidar system 100 may include one or more lenses to focus the inputbeam 135 onto an active region of receiver 140. As another example, thelidar system 100 may include one or more flat mirrors or curved mirrors(e.g., concave, convex, or parabolic mirrors) to steer or focus theoutput beam 125 or the input beam 135. For example, the lidar system 100may include an off-axis parabolic mirror to focus the input beam 135onto an active region of receiver 140. As illustrated in FIG. 1, thelidar system 100 may include mirror 115 (which may be a metallic ordielectric mirror), and mirror 115 may be configured so that light beam125 passes through the mirror 115. As an example, mirror 115 (which maybe referred to as an overlap mirror, superposition mirror, orbeam-combiner mirror) may include a hole, slot, or aperture which outputlight beam 125 passes through. As another example, mirror 115 may beconfigured so that at least 80% of output beam 125 passes through mirror115 and at least 80% of input beam 135 is reflected by mirror 115. Inparticular embodiments, mirror 115 may provide for output beam 125 andinput beam 135 to be substantially coaxial so that the two beams travelalong substantially the same optical path (albeit in oppositedirections).

In particular embodiments, lidar system 100 may include a scanner 120 tosteer the output beam 125 in one or more directions downrange. As anexample, scanner 120 may include one or more scanning mirrors that areconfigured to rotate, tilt, pivot, or move in an angular manner aboutone or more axes. In particular embodiments, a flat scanning mirror maybe attached to a scanner actuator or mechanism which scans the mirrorover a particular angular range. As an example, scanner 120 may includea galvanometer scanner, a resonant scanner, a piezoelectric actuator, apolygonal scanner, a rotating-prism scanner, a voice coil motor, a DCmotor, a stepper motor, or a microelectromechanical systems (MEMS)device, or any other suitable actuator or mechanism. In particularembodiments, scanner 120 may be configured to scan the output beam 125over a 5-degree angular range, 20-degree angular range, 30-degreeangular range, 60-degree angular range, or any other suitable angularrange. As an example, a scanning mirror may be configured toperiodically rotate over a 15-degree range, which results in the outputbeam 125 scanning across a 30-degree range (e.g., a Θ-degree rotation bya scanning mirror results in a 2Θ-degree angular scan of output beam125). In particular embodiments, a field of regard (FOR) of a lidarsystem 100 may refer to an area or angular range over which the lidarsystem 100 may be configured to scan or capture distance information. Asan example, a lidar system 100 with an output beam 125 with a 30-degreescanning range may be referred to as having a 30-degree angular field ofregard. As another example, a lidar system 100 with a scanning mirrorthat rotates over a 30-degree range may produce an output beam 125 thatscans across a 60-degree range (e.g., a 60-degree FOR). In particularembodiments, lidar system 100 may have a FOR of approximately 10°, 20°,40°, 60°, 120°, or any other suitable FOR.

In particular embodiments, scanner 120 may be configured to scan theoutput beam 125 horizontally and vertically, and lidar system 100 mayhave a particular FOR along the horizontal direction and anotherparticular FOR along the vertical direction. As an example, lidar system100 may have a horizontal FOR of 10° to 120° and a vertical FOR of 2° to45°. In particular embodiments, scanner 120 may include a first mirrorand a second mirror, where the first mirror directs the output beam 125toward the second mirror, and the second mirror directs the output beam125 downrange. As an example, the first mirror may scan the output beam125 along a first direction, and the second mirror may scan the outputbeam 125 along a second direction that is substantially orthogonal tothe first direction. As another example, the first mirror may scan theoutput beam 125 along a substantially horizontal direction, and thesecond mirror may scan the output beam 125 along a substantiallyvertical direction (or vice versa). In particular embodiments, scanner120 may be referred to as a beam scanner, optical scanner, or laserscanner.

In particular embodiments, one or more scanning mirrors may becommunicatively coupled to controller 150 which may control the scanningmirror(s) so as to guide the output beam 125 in a desired directiondownrange or along a desired scan pattern. In particular embodiments, ascan pattern (which may be referred to as an optical scan pattern,optical scan path, or scan path) may refer to a pattern or path alongwhich the output beam 125 is directed. As an example, scanner 120 mayinclude two scanning mirrors configured to scan the output beam 125across a 60° horizontal FOR and a 20° vertical FOR. The two scannermirrors may be controlled to follow a scan path that substantiallycovers the 60°×20° FOR. As an example, the scan path may result in apoint cloud with pixels that substantially cover the 60°×20° FOR. Thepixels may be approximately evenly distributed across the 60°×20° FOR.Alternately, the pixels may have a particular nonuniform distribution(e.g., the pixels may be distributed across all or a portion of the60°×20° FOR, and the pixels may have a higher density in one or moreparticular regions of the 60°×20° FOR).

In particular embodiments, receiver 140 may be referred to as aphotoreceiver, optical receiver, optical sensor, detector,photodetector, or optical detector. In particular embodiments, lidarsystem 100 may include a receiver 140 that receives or detects at leasta portion of input beam 135 and produces an electrical signal thatcorresponds to input beam 135. As an example, if input beam 135 includesan optical pulse, then receiver 140 may produce an electrical current orvoltage pulse that corresponds to the optical pulse detected by receiver140. As another example, receiver 140 may include one or more avalanchephotodiodes (APDs) or one or more single-photon avalanche diodes(SPADs). As another example, receiver 140 may include one or more PNphotodiodes (e.g., a photodiode structure formed by a p-typesemiconductor and a n-type semiconductor) or one or more PIN photodiodes(e.g., a photodiode structure formed by an undoped intrinsicsemiconductor region located between p-type and n-type regions).Receiver 140 may have an active region or an avalanche-multiplicationregion that includes silicon, germanium, or InGaAs. The active region ofreceiver 140 may have any suitable size, such as for example, a diameteror width of approximately 50-500 μm. In particular embodiments, receiver140 may include circuitry that performs signal amplification, sampling,filtering, signal conditioning, analog-to-digital conversion,time-to-digital conversion, pulse detection, threshold detection,rising-edge detection, or falling-edge detection. As an example,receiver 140 may include a transimpedance amplifier that converts areceived photocurrent (e.g., a current produced by an APD in response toa received optical signal) into a voltage signal. The voltage signal maybe sent to pulse-detection circuitry that produces an analog or digitaloutput signal 145 that corresponds to one or more characteristics (e.g.,rising edge, falling edge, amplitude, or duration) of a received opticalpulse. As an example, the pulse-detection circuitry may perform atime-to-digital conversion to produce a digital output signal 145. Theelectrical output signal 145 may be sent to controller 150 forprocessing or analysis (e.g., to determine a time-of-flight valuecorresponding to a received optical pulse).

In particular embodiments, controller 150 may be electrically coupled orcommunicatively coupled to light source 110, scanner 120, or receiver140. As an example, controller 150 may receive electrical trigger pulsesor edges from light source 110, where each pulse or edge corresponds tothe emission of an optical pulse by light source 110. As anotherexample, controller 150 may provide instructions, a control signal, or atrigger signal to light source 110 indicating when light source 110should produce optical pulses. Controller 150 may send an electricaltrigger signal that includes electrical pulses, where each electricalpulse results in the emission of an optical pulse by light source 110.In particular embodiments, the frequency, period, duration, pulseenergy, peak power, average power, or wavelength of the optical pulsesproduced by light source 110 may be adjusted based on instructions, acontrol signal, or trigger pulses provided by controller 150. Inparticular embodiments, controller 150 may be coupled to light source110 and receiver 140, and controller 150 may determine a time-of-flightvalue for an optical pulse based on timing information associated withwhen the pulse was emitted by light source 110 and when a portion of thepulse (e.g., input beam 135) was detected or received by receiver 140.In particular embodiments, controller 150 may include circuitry thatperforms signal amplification, sampling, filtering, signal conditioning,analog-to-digital conversion, time-to-digital conversion, pulsedetection, threshold detection, rising-edge detection, or falling-edgedetection.

In particular embodiments, a lidar system 100 may be used to determinethe distance to one or more downrange targets 130. By scanning the lidarsystem 100 across a field of regard, the system can be used to map thedistance to a number of points within the field of regard. Each of thesedepth-mapped points may be referred to as a pixel. A collection ofpixels captured in succession (which may be referred to as a depth map,a point cloud, or a frame) may be rendered as an image or may beanalyzed to identify or detect objects or to determine a shape ordistance of objects within the FOR. As an example, a depth map may covera field of regard that extends 60° horizontally and 15° vertically, andthe depth map may include a frame of 100-2000 pixels in the horizontaldirection by 4-400 pixels in the vertical direction.

In particular embodiments, lidar system 100 may be configured torepeatedly capture or generate point clouds of a field of regard at anysuitable frame rate between approximately 0.1 frames per second (FPS)and approximately 1,000 FPS. As an example, lidar system 100 maygenerate point clouds at a frame rate of approximately 0.1 FPS, 0.5 FPS,1 FPS, 2 FPS, 5 FPS, 10 FPS, 20 FPS, 100 FPS, 500 FPS, or 1,000 FPS. Asanother example, lidar system 100 may be configured to produce opticalpulses at a rate of 5×10⁵ pulses/second (e.g., the system may determine500,000 pixel distances per second) and scan a frame of 1000×50 pixels(e.g., 50,000 pixels/frame), which corresponds to a point-cloud framerate of 10 frames per second (e.g., 10 point clouds per second). Inparticular embodiments, a point-cloud frame rate may be substantiallyfixed, or a point-cloud frame rate may be dynamically adjustable. As anexample, a lidar system 100 may capture one or more point clouds at aparticular frame rate (e.g., 1 Hz) and then switch to capture one ormore point clouds at a different frame rate (e.g., 10 Hz). A slowerframe rate (e.g., 1 Hz) may be used to capture one or morehigh-resolution point clouds, and a faster frame rate (e.g., 10 Hz) maybe used to rapidly capture multiple lower-resolution point clouds.

In particular embodiments, a lidar system 100 may be configured tosense, identify, or determine distances to one or more targets 130within a field of regard. As an example, a lidar system 100 maydetermine a distance to a target 130, where all or part of the target130 is contained within a field of regard of the lidar system 100. Inparticular embodiments, target 130 may include all or part of an objectthat is moving or stationary relative to lidar system 100. As anexample, target 130 may include all or a portion of a person, vehicle,motorcycle, truck, train, bicycle, wheelchair, pedestrian, animal, roadsign, traffic light, lane marking, road-surface marking, parking space,pylon, guard rail, traffic barrier, pothole, railroad crossing, obstaclein or near a road, curb, stopped vehicle on or beside a road, utilitypole, house, building, trash can, mailbox, tree, any other suitableobject, or any suitable combination of all or part of two or moreobjects.

In particular embodiments, one or more lidar systems 100 may beintegrated into a vehicle. As an example, multiple lidar systems 100 maybe integrated into a car to provide a complete 360-degree horizontal FORaround the car. As another example, 6-10 lidar systems 100, each systemhaving a 45-degree to 90-degree horizontal FOR, may be combined togetherto form a sensing system that provides a point cloud covering a360-degree horizontal FOR. The lidar systems 100 may be oriented so thatadjacent FORs have an amount of spatial or angular overlap to allow datafrom the multiple lidar systems 100 to be combined or stitched togetherto form a single or continuous 360-degree point cloud. As an example,the FOR of each lidar system 100 may have approximately 1-15 degrees ofoverlap with an adjacent FOR. In particular embodiments, a vehicle mayrefer to a mobile machine configured to transport people or cargo. Forexample, a vehicle may include, may take the form of, or may be referredto as a car, automobile, motor vehicle, truck, bus, van, trailer,off-road vehicle, farm vehicle, lawn mower, construction equipment, golfcart, motorhome, taxi, motorcycle, scooter, bicycle, skateboard, train,snowmobile, watercraft (e.g., a ship or boat), aircraft (e.g., afixed-wing aircraft, helicopter, or dirigible), or spacecraft. Inparticular embodiments, a vehicle may include an internal combustionengine or an electric motor that provides propulsion for the vehicle.

In particular embodiments, one or more lidar systems 100 may be includedin a vehicle as part of an advanced driver assistance system (ADAS) toassist a driver of the vehicle in the driving process. For example, alidar system 100 may be part of an ADAS that provides information orfeedback to a driver (e.g., to alert the driver to potential problems orhazards) or that automatically takes control of part of a vehicle (e.g.,a braking system or a steering system) to avoid collisions or accidents.A lidar system 100 may be part of a vehicle ADAS that provides adaptivecruise control, automated braking, automated parking, collisionavoidance, alerts the driver to hazards or other vehicles, maintains thevehicle in the correct lane, or provides a warning if an object oranother vehicle is in a blind spot.

In particular embodiments, one or more lidar systems 100 may beintegrated into a vehicle as part of an autonomous-vehicle drivingsystem. As an example, a lidar system 100 may provide information aboutthe surrounding environment to a driving system of an autonomousvehicle. An autonomous-vehicle driving system may include one or morecomputing systems that receive information from a lidar system 100 aboutthe surrounding environment, analyze the received information, andprovide control signals to the vehicle's driving systems (e.g., steeringwheel, accelerator, brake, or turn signal). As an example, a lidarsystem 100 integrated into an autonomous vehicle may provide anautonomous-vehicle driving system with a point cloud every 0.1 seconds(e.g., the point cloud has a 10 Hz update rate, representing 10 framesper second). The autonomous-vehicle driving system may analyze thereceived point clouds to sense or identify targets 130 and theirrespective distances or speeds, and the autonomous-vehicle drivingsystem may update control signals based on this information. As anexample, if lidar system 100 detects a vehicle ahead that is slowingdown or stopping, the autonomous-vehicle driving system may sendinstructions to release the accelerator and apply the brakes.

In particular embodiments, an autonomous vehicle may be referred to asan autonomous car, driverless car, self-driving car, robotic car, orunmanned vehicle. In particular embodiments, an autonomous vehicle mayrefer to a vehicle configured to sense its environment and navigate ordrive with little or no human input. As an example, an autonomousvehicle may be configured to drive to any suitable location and controlor perform all safety-critical functions (e.g., driving, steering,braking, parking) for the entire trip, with the driver not expected tocontrol the vehicle at any time. As another example, an autonomousvehicle may allow a driver to safely turn their attention away fromdriving tasks in particular environments (e.g., on freeways), or anautonomous vehicle may provide control of a vehicle in all but a fewenvironments, requiring little or no input or attention from the driver.

In particular embodiments, an autonomous vehicle may be configured todrive with a driver present in the vehicle, or an autonomous vehicle maybe configured to operate the vehicle with no driver present. As anexample, an autonomous vehicle may include a driver's seat withassociated controls (e.g., steering wheel, accelerator pedal, and brakepedal), and the vehicle may be configured to drive with no one seated inthe driver's seat or with little or no input from a person seated in thedriver's seat. As another example, an autonomous vehicle may not includeany driver's seat or associated driver's controls, and the vehicle mayperform substantially all driving functions (e.g., driving, steering,braking, parking, and navigating) without human input. As anotherexample, an autonomous vehicle may be configured to operate without adriver (e.g., the vehicle may be configured to transport humanpassengers or cargo without a driver present in the vehicle). As anotherexample, an autonomous vehicle may be configured to operate without anyhuman passengers (e.g., the vehicle may be configured for transportationof cargo without having any human passengers onboard the vehicle).

FIG. 2 illustrates an example scan pattern 200 produced by a lidarsystem 100. In particular embodiments, a lidar system 100 may beconfigured to scan output optical beam 125 along one or more particularscan patterns 200. In particular embodiments, a scan pattern 200 mayhave any suitable horizontal FOR (FOR_(H)) and any suitable vertical FOR(FOR_(V)). For example, a scan pattern 200 may have a field of regard(e.g., FOR_(H)×FOR_(V)) of 40°×30°, 90°×40°, or 60°×15°. As anotherexample, a scan pattern 200 may have a FOR_(H) greater than or equal to10°, 25°, 30°, 40°, 60°, 90°, or 120°. As another example, a scanpattern 200 may have a FOR_(V) greater than or equal to 2°, 5°, 10°,15°, 20°, 30°, or 45°. In the example of FIG. 2, reference line 220represents a center of the field of regard of scan pattern 200. Inparticular embodiments, reference line 220 may have any suitableorientation, such as for example, a horizontal angle of 0° (e.g.,reference line 220 may be oriented straight ahead) and a vertical angleof 0° (e.g., reference line 220 may have an inclination of 0°), orreference line 220 may have a nonzero horizontal angle or a nonzeroinclination (e.g., a vertical angle of +10° or −10°). In FIG. 2, if thescan pattern 200 has a 60°×15° field of regard, then scan pattern 200covers a ±30° horizontal range with respect to reference line 220 and a±7.5° vertical range with respect to reference line 220. Additionally,optical beam 125 in FIG. 2 has an orientation of approximately −15°horizontal and +3° vertical with respect to reference line 220. Opticalbeam 125 may be referred to as having an azimuth of −15° and an altitudeof +3° relative to reference line 220. In particular embodiments, anazimuth (which may be referred to as an azimuth angle) may represent ahorizontal angle with respect to reference line 220, and an altitude(which may be referred to as an altitude angle, elevation, or elevationangle) may represent a vertical angle with respect to reference line220.

In particular embodiments, a scan pattern 200 may include multiplepixels 210, and each pixel 210 may be associated with one or more laserpulses and one or more corresponding distance measurements. Inparticular embodiments, a cycle of scan pattern 200 may include a totalof P_(x)×P_(y) pixels 210 (e.g., a two-dimensional distribution of P_(x)by P_(y) pixels). As an example, scan pattern 200 may include adistribution with dimensions of approximately 100-2,000 pixels 210 alonga horizontal direction and approximately 4-400 pixels 210 along avertical direction. As another example, scan pattern 200 may include adistribution of 1,000 pixels 210 along the horizontal direction by 64pixels 210 along the vertical direction (e.g., the frame size is 1000×64pixels) for a total of 64,000 pixels per cycle of scan pattern 200. Inparticular embodiments, the number of pixels 210 along a horizontaldirection may be referred to as a horizontal resolution of scan pattern200, and the number of pixels 210 along a vertical direction may bereferred to as a vertical resolution. As an example, scan pattern 200may have a horizontal resolution of greater than or equal to 100 pixels210 and a vertical resolution of greater than or equal to 4 pixels 210.As another example, scan pattern 200 may have a horizontal resolution of100-2,000 pixels 210 and a vertical resolution of 4-400 pixels 210.

In particular embodiments, each pixel 210 may be associated with adistance (e.g., a distance to a portion of a target 130 from which anassociated laser pulse was scattered) or one or more angular values. Asan example, a pixel 210 may be associated with a distance value and twoangular values (e.g., an azimuth and altitude) that represent theangular location of the pixel 210 with respect to the lidar system 100.A distance to a portion of target 130 may be determined based at leastin part on a time-of-flight measurement for a corresponding pulse. Anangular value (e.g., an azimuth or altitude) may correspond to an angle(e.g., relative to reference line 220) of output beam 125 (e.g., when acorresponding pulse is emitted from lidar system 100) or an angle ofinput beam 135 (e.g., when an input signal is received by lidar system100). In particular embodiments, an angular value may be determinedbased at least in part on a position of a component of scanner 120. Asan example, an azimuth or altitude value associated with a pixel 210 maybe determined from an angular position of one or more correspondingscanning mirrors of scanner 120.

FIG. 3 illustrates an example lidar system 100 that includes a laser300, sensor 310, and laser-sensor link 320. In particular embodiments,laser 300 may be configured to emit pulses of light and may be referredto as a laser system, laser head, or light source. In particularembodiments, laser 300 may include, may be part of, may be similar to,or may be substantially the same as light source 110 illustrated in FIG.1 and described above. Additionally, the lidar system 100 in FIG. 3 mayinclude components similar to those of lidar system 100 in FIG. 1 (e.g.,mirror 115, scanner 120, receiver 140, or controller 150). In theexample of FIG. 3, laser 300 is coupled to a remotely located sensor 310by a laser-sensor link 320 (which may be referred to as a link). Inparticular embodiments, sensor 310 may be referred to as a sensor headand may include a mirror 115, scanner 120, receiver 140, or controller150. As an example, laser 300 may include a pulsed laser diode (e.g., apulsed DFB laser) followed by an optical amplifier, and light from thelaser 300 may be conveyed by an optical fiber of laser-sensor link 320to a scanner 120 in a remotely located sensor 310. A length oflaser-sensor link 320 or a separation distance between laser 300 andsensor 310 may be approximately 0.5 m, 1 m, 2 m, 5 m, 10 m, 20 m, 50 m,100 m, or any other suitable distance.

FIG. 4 illustrates an example lidar system 100 where the laser-sensorlink 320 includes an optical link 330 and an electrical link 350 coupledbetween the laser 300 and the sensor 310. The lidar system 100 in FIG. 4includes a light source (e.g., laser 300) that is located remotely froma sensor head 310, where the sensor head 310 includes other lidar-systemcomponents (e.g., output collimator 340, mirror 115, scanner 120,receiver 140, and controller 150). In particular embodiments, alaser-sensor link 320 may refer to a cable harness, conduit, or assemblythat provides an optical or electrical connection between a light source(e.g., laser 300) and a sensor head 310. A laser-sensor link 320 mayhave any suitable length (e.g., a length greater than or equal to 0.5 m,1 m, 2 m, 5 m, 10 m, 20 m, 50 m, or 100 m) and may be used to sendoptical or electrical signals from laser 300 to sensor 310 or fromsensor 310 to laser 300. A laser-sensor link 320 may include anysuitable number of optical links 330 (e.g., 0, 1, 2, 3, 5, or 10 opticallinks 330) or any suitable number of electrical links 350 (e.g., 0, 1,2, 3, 5, or 10 electrical links 350). In FIG. 4, the laser-sensor link320 includes one optical link 330 from laser 300 to output collimator340 and one electrical link 350 that connects laser 300 and controller150. Each optical link 330 and each electrical link 350 of alaser-sensor link 320 may have any suitable length, such as for example,a length of approximately 0.5 m, 1 m, 2 m, 5 m, 10 m, 20 m, 50 m, or 100m. As an example, laser 300 and sensor 310 may be located approximately4 meters apart, and a fiber-optic cable 330 that conveys light fromlaser 300 to sensor 310 may have a length of greater than or equal to 4meters.

In particular embodiments, an optical link 330 may include optical fiber(which may be referred to as fiber-optic cable or fiber) that conveys,carries, transports, or transmits light between a laser 300 and a sensor310. As an example, optical link 330 (which may be referred to as afiber-optic link or a fiber link) may include any suitable type ofoptical fiber, such as for example, single-mode (SM) fiber, multi-mode(MM) fiber, large-mode-area (LMA) fiber, polarization-maintaining (PM)fiber, photonic-crystal or photonic-bandgap fiber, gain fiber (e.g.,rare-earth-doped optical fiber for use in an optical amplifier), or anysuitable combination thereof. As another example, optical link 330 mayinclude a glass SM fiber with a core diameter of approximately κ μm anda cladding diameter of approximately 125 μm. As another example, opticallink 330 may include a photonic-crystal fiber or a photonic-bandgapfiber in which light is confined or guided by an arrangement of airholes distributed along the length of a glass fiber. In particularembodiments, an optical link 330 may include a fiber-optic cable that iscoupled to, attached to, or terminated at an output collimator 340. InFIG. 4, optical link 330 conveys optical pulses (which are emitted bylaser 300) to sensor head 310, and the optical link 330 is terminated atoutput collimator 340. The output collimator 340 may include a lens or afiber-optic collimator that receives light from a fiber-optic cable 330and produces a free-space optical beam 125. In FIG. 4, output collimator340 receives optical pulses conveyed from laser 300 by optical link 330and produces a free-space optical beam 125 that includes the opticalpulses. The output collimator 340 directs the free-space optical beam125 through mirror 115 and to scanner 120.

In particular embodiments, an electrical link 350 may include electricalwire or cable that conveys or transmits electrical power or one or moreelectrical signals between laser 300 and sensor 310. In particularembodiments, an electrical link 350 may convey electrical power tosensor 310 from laser 300, or vice versa. As an example, laser 300 mayinclude a power supply or a power conditioner that provides electricalpower to the laser 300, and additionally, the power supply or powerconditioner may provide power to one or more components of sensor 310(e.g., scanner 120, receiver 140, or controller 150) via one or moreelectrical links 350.

In particular embodiments, electrical link 350 may convey one or moreelectrical signals from laser 300 to sensor 310, or vice versa. Theelectrical signals may include data or information in the form of ananalog or digital signal. As an example, an electrical link 350 mayinclude a coaxial cable or twisted-pair cable configured to transmit ananalog or digital signal from receiver 140 or controller 150 to acontroller or processor located in laser 300. As another example, anelectrical link 350 may convey instructions or a drive signal forscanner 120 from a controller or processor located in laser 300 tosensor 310. As another example, all or part of a controller or processormay be located in laser 300, and one or more electrical links 350 mayconvey signals to or from scanner 120, receiver 140, or controller 150located in sensor 310. As another example, an electrical link 350 mayprovide an interlock signal from sensor 310 to laser 300. If controller150 detects a fault condition indicating a problem with the lidar system100, the controller 150 may change a voltage on an interlock line (e.g.,from 5 V to 0 V) indicating that laser 300 should shut down, stopemitting light, or reduce the power or energy of emitted light. A faultcondition may be triggered by a failure of scanner 120, by a failure ofreceiver 140, or by a person or object coming within a thresholddistance of sensor 310 (e.g., within 0.1 m, 0.5 m, 1 m, 5 m, or anyother suitable distance).

In particular embodiments, sensor head 310 may include a scanner 120configured to scan pulses of light across a field of regard of thesensor head 310. The scanned pulses of light may include pulses of lightemitted by laser 300 and conveyed from the laser 300 to the sensor 310by fiber-optic cable 330 of optical link 320. In particular embodiments,sensor head 310 may include a receiver 140 configured to detect at leasta portion of the scanned pulses of light scattered or reflected by atarget 130 located downrange from the sensor head 310. The target 130may be at least partially contained within a field of regard of thesensor head 310 and located a distance D from the sensor head 310 thatis less than or equal to a maximum range R_(MAX) of the lidar system100. In particular embodiments, a maximum range (which may be referredto as a maximum distance) of a lidar system 100 may refer to the maximumdistance over which the lidar system 100 is configured to sense oridentify targets 130 that appear in a field of regard of the lidarsystem 100. The maximum range of lidar system 100 may be any suitabledistance, such as for example, 25 m, 50 m, 100 m, 200 m, 500 m, or 1 km.As an example, a lidar system 100 with a 200-m maximum range may beconfigured to sense or identify various targets 130 located up to 200 maway from a sensor head 310 of the lidar system 100. For a lidar system100 with a 200-m maximum range (R_(MAX)=200 m), the time of flightcorresponding to the maximum range is approximately 2·R_(MAX)/c≅1.33 μs.

In particular embodiments, lidar system 100 may include one or moreprocessors (e.g., controller 150) configured to determine a distance Dfrom sensor 310 to a target 130 based at least in part on a time offlight for a pulse of light to travel from the sensor 310 to the target130 and back to the sensor 310. As an example, a controller 150 may belocated in laser 300 or in sensor 310, or parts of a controller 150 maybe distributed between laser 300 and sensor 310. As another example,lidar system 100 may include two or more processors (e.g., one processormay be located in laser 300 and another processor may be located insensor 310). A time-of-flight value or a distance from sensor 310 totarget 130 may be determined by a controller 150 located in laser 300 orsensor 310. Alternately, a time-of-flight value or a distance to target130 may be determined by a combination of devices located in laser 300and sensor 310. As an example, each sensor head 310 of a lidar system100 may include electronics (e.g., an electronic filter, transimpedanceamplifier, threshold detector, or time-to-digital (TDC) converter)configured to receive or process a signal from receiver 140 or from anAPD or SPAD of receiver 140. Additionally, laser 300 may includeprocessing electronics configured to determine a time-of-flight value ora distance to target 130 based on a signal received from a sensor head310 via an electrical link 350.

A lidar system 100 as described or illustrated herein may also includevarious elements described or illustrated in U.S. Provisional PatentApplication No. 62/243,633, filed Oct. 19, 2015 and entitled “LidarSystem with Improved Signal-to-Noise Ratio in the Presence of SolarBackground Noise” or U.S. Provisional Patent Application No. 62/251,672,filed Nov. 5, 2015 and entitled “Lidar System with Improved ScanningSpeed for High-Resolution Depth Mapping,” each of which is incorporatedherein by reference.

FIG. 5 illustrates an example lidar system 100 with a laser 300 coupledto multiple sensor heads (310-1, 310-2, . . . , 310-N) by multiplerespective laser-sensor links (320-1, 320-2, . . . , 320-N). Inparticular embodiments, each laser-sensor link 320 may couple laser 300to a corresponding sensor head 310, and each laser-sensor link 320 mayinclude an optical link 330 configured to convey pulses of light fromlaser 300 to the corresponding sensor head 310. In FIG. 5, thelaser-sensor links 320-1 through 320-N may each include a fiber-opticcable having a length greater than or equal to 1 meter. In particularembodiments, a lidar system 100 may include a laser 300 coupled to 1, 2,4, 6, 8, 10, 20, or any other suitable number of sensor heads 310. InFIG. 5, lidar system 100 includes N laser-sensor links 320 which couplelaser 300 to N respective sensor heads 310. In FIG. 5, laser-sensor link320-1 couples laser 300 to sensor 310-1, laser-sensor link 320-2 coupleslaser 300 to sensor 310-2, and laser-sensor link 320-N couples laser 300to sensor 310-N. In particular embodiments, each laser-sensor link 320may be configured to convey at least a portion of pulses of lightemitted by laser 300 to a corresponding sensor head 310. As an example,in FIG. 5, lidar system 100 may include six laser-sensor links 320 andsix sensors 310 (e.g., N=6), and each pulse emitted by laser 300 may besplit between each of the six sensor heads 310. As another example, eachpulse emitted by laser 300 may be directed to a particular sensor headso that each sensor head receives one out of every six pulses emitted bylaser 300 (e.g., the 1^(st), 7^(th), 13^(th), . . . pulses may beconveyed to sensor 310-1; the 2^(nd), 8^(th), 14^(th), . . . pulses maybe conveyed to sensor 310-2; etc.).

FIG. 6 illustrates an example vehicle with a lidar system that includesa laser 300 with multiple sensor heads 310 coupled to the laser 300 bymultiple laser-sensor links 320. In particular embodiments, eachlaser-sensor link 320 may include one or more optical links 330 or oneor more electrical links 350. As an example, each laser-sensor link 320may include an optical link 330 configured to convey at least a portionof the pulses of light emitted by laser 300 to a corresponding sensorhead 310. Additionally, each sensor head 310 may include a scanner 120configured to scan the pulses of light conveyed from the laser 300 tothe sensor head 310 by the corresponding optical link 330. As anotherexample, each laser-sensor link 320 may include one or more electricallinks 350 that convey electrical power or signals between laser 300 anda corresponding sensor head 310.

In particular embodiments, a lidar system 100 may be incorporated into avehicle, and sensor heads 310 may be positioned or oriented to provide agreater than or equal to 30-degree view of an environment around thevehicle. As an example, a lidar system 100 with multiple sensor heads310 may provide a horizontal field of regard around a vehicle ofapproximately 30°, 45°, 60°, 90°, 120°, 180°, 270°, or 360°. Each sensorhead 310 may be attached to or incorporated into a bumper, fender,grill, side panel, spoiler, roof, headlight assembly, taillightassembly, rear-view mirror assembly, hood, trunk, window, or any othersuitable part of a vehicle. In the example of FIG. 6, four sensor heads310 are positioned at or near the four corners of the vehicle (e.g., thesensor heads may be incorporated into a light assembly, side panel,bumper, or fender), and laser 300 may be located within the vehicle(e.g., in or near the trunk). The four sensor heads 310 may each providea 90° to 120° horizontal field of regard (FOR), and the four sensorheads 310 may be oriented so that together they provide a complete360-degree view around the vehicle. As another example, a lidar system100 may include six sensor heads 310 positioned on or around a vehicle,where each sensor head 310 provides a 60° to 90° horizontal FOR. Asanother example, a lidar system 100 may include eight sensor heads 310,and each sensor head 310 may provide a 45° to 60° horizontal FOR. Asanother example, a lidar system 100 may include six sensor heads 310,where each sensor head 310 provides a 70° horizontal FOR with an overlapbetween adjacent FORs of approximately 10°. As another example, a lidarsystem 100 may include two sensor heads 310 which together provide aforward-facing horizontal FOR of greater than or equal to 30°. Inparticular embodiments, data from each of multiple sensor heads 310 maybe combined or stitched together to generate a point cloud that covers agreater than or equal to 30-degree horizontal view around a vehicle. Asan example, laser 300 may include a controller or processor thatreceives data from each sensor head 310 (e.g., via a correspondingelectrical link 350) and processes the received data to construct apoint cloud covering a 360-degree horizontal view around a vehicle or todetermine distances to one or more targets 130.

FIG. 7 illustrates an example laser 300 with a seed laser 400 and ademultiplexer 410 that distributes light from the seed laser to multipleoptical links (330-1, 330-2, . . . , 330-N). Each optical link conveyslight received from the demultiplexer 410 to a corresponding sensor head(e.g., optical link 330-1 conveys light to sensor head 310-1, etc.). Inparticular embodiments, demultiplexer 410 may include an optical-powersplitter, an optical switch, a wavelength demultiplexer, or any suitablecombination thereof. In particular embodiments, seed laser 400 mayproduce optical pulses, and laser 300 may also include one or moreoptical amplifiers (not illustrated in FIG. 7) to amplify the seed-laserpulses. In particular embodiments, a lidar system 100 may include Noptical links (330-1, 330-2, . . . , 330-N) coupled to N respectivesensor heads (310-1, 310-2, . . . , 310-N), and laser 300 may include a1×N optical demultiplexer 410 configured to distribute pulses of lightbetween the N optical links. The pulses of light distributed to theoptical links may be pulses directly emitted by the seed laser 400 orpulses that are emitted by the seed laser 400 and then amplified by oneor more optical amplifiers.

In particular embodiments, each optical link (330-1, 330-2, . . . ,330-N) may be approximately the same length, or the optical links mayhave two or more different lengths. As an example, each optical link mayinclude a fiber-optic cable with a length of approximately 20 m. Asanother example, the optical links may each include a fiber-optic cablewith a particular or different length (e.g., two of the optical linksmay include a 5-m fiber, another two optical links may include a 10-mfiber, and one optical link may include a 20-m fiber). In particularembodiments, the sensor heads (310-1, 310-2, . . . , 310-N) may emitoptical pulses at substantially the same time or at different times withrespect to each other. As an example, a demultiplexer 410 may split asingle optical pulse into N optical pulses. The N optical pulses may beconveyed to the N sensor heads by fiber-optic cables havingsubstantially the same length, and the pulses may be emitted by thesensor heads at approximately the same time. As another example, the Noptical pulses may be conveyed to the N sensor heads by fiber-opticcables having two or more different lengths, and, due to the differentpropagation times associated with the different fiber lengths, thepulses may be emitted at different times. As another example, thedemultiplexer 410 may direct different optical pulses to differentsensor heads at different times, resulting in the pulses being emittedby the sensor heads at different times. In particular embodiments, sinceeach sensor head may emit and receive pulses independent of other sensorheads, the operation of a lidar system 100 as described and illustratedherein may not specifically depend on whether the pulses are emitted ina time-synchronous fashion or the pulses are emitted without regard tothe relative time synchronization.

In particular embodiments, demultiplexer 410 may include a 1×Nfiber-optic power splitter with one fiber-optic input port and Nfiber-optic output ports. As an example, an optical-power splitter mayinclude one or more fused biconical taper (FBT) splitters which areassembled by placing two or more fibers adjacent to one another and thenfusing the fibers together by applying heat. As another example, anoptical-power splitter may include a planar lightwave circuit (PLC) madeby fabricating optical waveguides on a glass substrate using alithographic process. In particular embodiments, a power splitter may bea passive optical device (e.g., requiring no electronics or electricalpower) configured to split each pulse of light received at an input portinto N pulses of light which are then sent to each of the respective Noutput ports. A 1×N optical-power splitter may send each pulse of the Npulses to a corresponding optical link (330-1, 330-2, . . . , 330-N) fortransmission to a corresponding sensor head (310-1, 310-2, . . . ,310-N).

In particular embodiments, a power splitter may split each receivedpulse of light substantially evenly into N pulses, where each of the Npulses has approximately 1/N of the energy or power of the receivedpulse of light. As an example, for a lidar system 100 with 8 sensorheads 310 (e.g., N=8), a demultiplexer 410 that includes a 1×8 powersplitter may split a received pulse into 8 pulses, and each of thosepulses may have approximately ⅛ of the pulse energy of the receivedpulse. If the received pulse has a pulse energy of 8 μJ, then each ofthe 8 pulses may have a pulse energy of approximately 1 μJ.

In particular embodiments, a power splitter may split each receivedpulse of light into N pulses with an unequal distribution of energy orpower between the N pulses. As an example, for a lidar system 100 with 6sensor heads 310, a power splitter may split each received optical pulseinto 2 high-energy pulses, 2 medium-energy pulses, and 2 low-energypulses. Each high-energy pulse may have approximately 25% of the energyof the received pulse, each medium-energy pulse may have approximately15% of the energy of the received pulse, and each low-energy pulse mayhave approximately 10% of the energy of the received pulse. As anotherexample, for a lidar system 100 with 8 sensor heads 310, a powersplitter may split a received pulse into 4 high-energy pulses and 4low-energy pulses. Each high-energy pulse may have approximately 15% to20% of the energy of the received pulse, and each low-energy pulse mayhave approximately κ% to 10% of the energy of the received pulse.Splitting an optical pulse in an unequal manner may allow a lidar system100 to supply higher-energy pulses to sensor heads 310 which are morecritical to the lidar-system performance. As an example, the 4high-energy pulses may be sent to sensor heads 310 that aresubstantially forward facing (e.g., facing in the direction of travel ofa vehicle), and the 4 low-energy pulses may be sent to side-facing orrear-facing sensor heads 310. An optical pulse with a higher energy mayprovide a sensor head 310 with a correspondingly longer maximum range ascompared to a lower-energy pulse. As an example, sensor heads 310supplied with high-energy pulses may have a maximum range ofapproximately 200 m, while sensor heads 310 supplied with low-energypulses may have a maximum range of approximately 100 m.

In particular embodiments, demultiplexer 410 may include a 1×N opticalswitch. As an example, demultiplexer 410 may include a fiber-opticswitch that allows light received at an input fiber-optic port to beselectively directed to one of N output fiber-optic ports. A 1×N opticalswitch may employ a switching mechanism that is based on mechanicalswitching, piezoelectric switching, thermal switching, liquid-crystalswitching, switching with a MEMS device, or switching between waveguidesin a PLC. A laser 300 may emit optical pulses with a pulse repetitionfrequency f, and a 1×N optical switch may sequentially switch theemitted pulses between each of the N optical links 330 (e.g., eachoptical link 330 receives one pulse for every N pulses emitted by laser300). Each sensor 310 may then perform lidar scanning with pulses havinga pulse repetition frequency of approximately f/N. As an example, iflaser 300 has a pulse repetition frequency of 3.6 MHz and lidar system100 has 6 sensor heads 310, then each sensor head 310 will receive everysixth pulse resulting in a sensor-head pulse repetition frequency ofapproximately 600 kHz. A demultiplexer 410 that sequentially switchesinput light to one of N output ports may be referred to as a temporaldemultiplexer.

In particular embodiments, demultiplexer 410 may include a wavelengthdemultiplexer, which may be referred to as a wavelength splitter, ademux, or a wavelength division multiplexer (WDM). As an example,demultiplexer 410 may include a 1×N fiber-optic wavelength demultiplexerthat receives light at N different wavelengths and directs the light toone of N output ports based on wavelength. A wavelength demultiplexermay perform wavelength splitting using a prism, diffraction grating,holographic grating, arrayed waveguide grating, or one or more dichroicfilters. In particular embodiments, a lidar system 100 may use anysuitable number of different wavelengths split between any suitablenumber of sensor heads 310. As an example, laser 300 may produce pulsesat N different wavelengths, and the pulses may be sent to N respectivesensor heads 310 according to wavelength. As another example, laser 300may produce pulses at N/2 different wavelengths, and the lidar system100 may include N sensor heads 310 (e.g., each pulse at a particularwavelength may be split between two sensor heads 310).

In particular embodiments, the pulses of light emitted by laser 300 mayhave N different wavelengths, and demultiplexer 410 may include awavelength demultiplexer that sends each pulse having a particularwavelength to a corresponding optical link 330 for transmission to acorresponding sensor head 310. As an example, laser 300 may include Nlaser diodes each configured to produce light at a particularwavelength, or laser 300 may include one wavelength-tunable laserconfigured to produce light at N different wavelengths. In particularembodiments, the N different wavelengths may have any suitablewavelength separation between adjacent wavelengths, such as for examplea wavelength separation of approximately 0.8 nm, 1.6 nm, 4 nm, or 10 nm.As an example, laser 300 may produce pulses at four differentwavelengths with a 1.6-nm wavelength separation (e.g., 1550.1 nm, 1551.7nm, 1553.3 nm, and 1554.9 nm), and the demultiplexer 410 may include a1×4 wavelength demultiplexer that sends each of the four differentwavelengths to a corresponding optical link 330. A laser 300 may produceoptical pulses at N different wavelengths (e.g., a repeating sequence ofpulses at wavelengths λ₁, λ₂, . . . , λ_(N)) with a pulse repetitionfrequency f. A 1×N wavelength demultiplexer may send each differentwavelength to a particular sensor head 310 (e.g., each sensor head 310receives one pulse for every N pulses emitted by laser 300), resultingin a sensor-head pulse repetition frequency of approximately f/N. As anexample, if laser 300 has a pulse repetition frequency of 4.8 MHz andproduces pulses at 8 different wavelengths (corresponding to 8 sensorheads 310), then each sensor head 310 will receive one out of eightpulses, resulting in a pulse repetition frequency for each sensor head310 of approximately 600 kHz.

In particular embodiments, demultiplexer 410 may include a combinationof one or more optical-power splitters, one or more optical switches, orone or more wavelength demultiplexers. As an example, demultiplexer 410may include a 1×m optical-power splitter followed by m 1×N/m opticalswitches. The parameters N and m may each have any suitable positiveinteger value (e.g., 1, 2, 3, 4, 6, 8, or 10), where N is greater thanm. If m=2 and N=8, then demultiplexer 410 includes a 1×2 power splitterfollowed by two 1×4 optical switches. As another example, demultiplexer410 may include a 1×m optical switch followed by m 1×N/m optical-powersplitters. If m=2 and N=6, then demultiplexer 410 includes a 1×2 opticalswitch followed by two 1×3 power splitters. The 1×2 optical switch mayalternate between directing pulses to one of its two output ports. Everyother pulse emitted by laser 300 may be directed to one of the twooutput ports, and each pulse is then split into three pulses by one ofthe 1×3 power splitters coupled to an output port of the switch. Asanother example, demultiplexer 410 may include a 1×m wavelength splitterfollowed by m 1×/N/m optical-power splitters, and laser 300 may producepulses at rn different wavelengths. If m=4 and N=8, then demultiplexer410 includes a 1×4 wavelength splitter followed by 4 1×2 optical-powersplitters, and laser 300 may produce pulses at 4 different wavelengths.As another example, demultiplexer 410 may include a 1×m optical-powersplitter followed by m 1×N/m wavelength splitters, and laser 300 mayproduce pulses at N/m different wavelengths. If m=4 and N=8, thendemultiplexer 410 includes a 1×4 optical-power splitter followed by four1×2 wavelength splitters. If laser 300 produces pulses at two differentwavelengths, then each pulse may be split into four pulses by the powersplitter, and each of the four pulses may be directed to one of twosensor heads 310 by the corresponding wavelength splitter.

FIG. 8 illustrates an example seed laser 400 that includes a laser diode440 driven by a pulse generator 430. Seed laser 400 or laser diode 440in FIG. 8 may be referred to as a pulsed laser or a pulsed laser diode.In particular embodiments, a seed laser 400 may include a functiongenerator 420, a pulse generator 430, a laser diode 440, or atemperature controller 450. In the example of FIG. 8, seed laser 400includes function generator 420 coupled to pulse generator 430, which isin turn coupled to laser diode 440. Additionally, temperature controller450 is coupled to laser diode 440. In particular embodiments, seed laser400 may produce optical seed pulses, which are emitted at the seed-laseroutput (which may be a free-space output or a fiber-optic output). Inparticular embodiments, the optical seed pulses may have a pulserepetition frequency of less than or equal to 100 MHz (e.g.,approximately 500 kHz, 640 kHz, 750 kHz, 1 MHz, 2 MHz, 4 MHz, 5 MHz, 10MHz, 20 MHz, 50 MHz, or 100 MHz), a pulse duration of less than or equalto 20 nanoseconds (e.g., approximately 200 ps, 400 ps, 500 ps, 800 ps, 1ns, 2 ns, 4 ns, 8 ns, 10 ns, 15 ns, or 20 ns), a duty cycle of less thanor equal to 1% (e.g., approximately 0.01%, 0.02%, 0.05%, 0.1%, 0.2%,0.5%, or 1%), or an operating wavelength of between 1400 nm and 2050 nm.As an example, the seed pulses may have a pulse repetition frequency of500-750 kHz, a pulse duration of less than or equal to 2 ns, and a dutycycle of less than or equal to 0.1%. As another example, the seed pulsesmay have a pulse repetition frequency of approximately 640 kHz, and apulse duration of approximately 1 ns (which corresponds to a duty cycleof approximately 0.064%). A duty cycle may be determined from the ratioof pulse duration to pulse period or from the product of pulse durationand pulse repetition frequency. The laser diode 440 may have anysuitable operating wavelength, such as for example, an operatingwavelength of approximately 1400 nm, 1500 nm, 1550 nm, 1600 nm, or 2000nm. In particular embodiments, the seed pulses may be relativelylow-power optical pulses, and the seed-laser output may be coupled toone or more optical amplifiers configured to amplify the low-powerpulses to produce amplified pulses of light which are emitted by laser300. As an example, the seed pulses may have an average power of greaterthan or equal to 1 μW. As another example, the seed pulses may have anaverage power of between approximately 0.1 μW and 10 μW.

In particular embodiments, seed laser 400 may include a laser diode 440that is electrically driven by pulse generator 430 to produce opticalseed pulses. In the example of FIG. 8, function generator 420 supplies avoltage signal 422 to pulse generator 430, and pulse generator 430drives laser diode 440 with a current signal 432. As an example,function generator 420 may produce a pulsed voltage signal with a pulserepetition frequency of between approximately 0.5 and 2 MHz and a pulseduration of approximately 500 ps. Pulse generator 430 may drive laserdiode 440 with a pulsed current signal 432 that corresponds to thevoltage signal 422 received from function generator 420. In particularembodiments, voltage signal 422 may include voltage pulses having anysuitable shape, such as for example, square-shaped pulses,triangle-shaped pulses, Gaussian-shaped pulses, or pulses having anarbitrary shape or a combination of shapes. In particular embodiments,current signal 432 may have a DC offset or may include current pulseshaving any suitable shape, such as for example, square-shaped pulses,triangle-shaped pulses, Gaussian-shaped pulses, or pulses having anarbitrary shape or a combination of shapes. The pulses of current signal432 may have a shape or duration similar to that of voltage signal 422.Additionally, laser diode 440 may emit optical pulses with a shape(e.g., square, triangle, Gaussian, or arbitrary) or duration that atleast approximately corresponds to the shape or duration of the currentpulses supplied by pulse generator 430.

In particular embodiments, laser diode 440 may be a Fabry-Perot laserdiode, a DFB laser, or a DBR laser. As an example, laser diode 440 maybe a DFB laser coupled to an optical fiber. Additionally, the lightemitted by laser diode 440 may pass through an optical isolator thatreduces the amount of back-reflected light that may be coupled back intothe laser diode 440. In particular embodiments, seed laser 400 mayinclude a single laser diode 440 having a substantially fixed operatingwavelength. As an example, laser diode 440 may be a single-wavelengthlaser configured to operate at a particular operating wavelength withlimited wavelength tunability. As another example, laser diode 440 mayinclude a DFB laser with an operating wavelength between approximately1400 nm and 1600 nm, and the DFB laser may be wavelength tunable over arange of approximately 4 nm (e.g., by adjusting the operatingtemperature of the laser diode 440).

In particular embodiments, laser diode 440 may operate withouttemperature control, or seed laser 400 may include a temperaturecontroller 450 to stabilize the operating temperature of laser diode440. As an example, the package or the semiconductor substrate of laserdiode 440 may be thermally coupled to a thermoelectric cooler (TEC)driven by temperature controller 450 to adjust or stabilize thelaser-diode operating temperature. The laser-diode operating temperaturemay be stabilized to within any suitable range of a target temperatureset point, such as for example, within approximately ±0.01° C., ±0.05°C., ±0.1° C., ±0.5° C., or ±1° C. of a target temperature. Stabilizationof the temperature of laser diode 440 may provide for the laser-diodeoperating wavelength to be substantially stable (e.g., the peakwavelength of laser diode 440 may vary by less than any suitable value,such as for example, less than approximately 0.1 nm, 0.5 nm, 1 nm, or 2nm). If lidar system 100 includes a narrow-band optical filter, then thelaser diode 440 may be temperature stabilized so as to match thelaser-diode operating wavelength to the passband of the optical filter.In particular embodiments, the temperature controller 450 may be used toadjust the operating wavelength of laser diode 440 by adjusting thelaser-diode set-point temperature. As an example, the laser diode 440may include a DFB laser with an operating wavelength that may betemperature tuned from approximately 1548 nm to approximately 1552 nm byadjusting the temperature set-point of the laser.

In particular embodiments, seed laser 400 may include awavelength-tunable laser configured to produce light at multiplewavelengths. As an example, a wavelength-tunable laser may produceoptical pulses at multiple wavelengths of light corresponding to themultiple sensor heads 310 of a lidar system 100. In particularembodiments, laser diode 440 may be a wavelength-tunable laser. As anexample, laser diode 440 may have an operating wavelength that may betunable over any suitable wavelength range, such as for example, 1 nm,10 nm, 20 nm, 50 nm, or 100 nm. As another example, laser diode 440 maybe tunable from approximately 1400 nm to approximately 1440 nm or fromapproximately 1530 nm to approximately 1560 nm. In particularembodiments, laser diode 440 may be an external-cavity diode laser whichincludes a laser diode and a wavelength-selective element, such as forexample, a diffraction grating or a grating structure integrated withinthe semiconductor structure of the laser diode. In particularembodiments, laser diode 440 may be configured to produce optical pulsesat multiple wavelengths. As an example, laser diode 440 may producesequences of N pulses having N different wavelengths. The pulses may beamplified and each pulse may be conveyed to one or more particularsensor heads 310 based on the wavelength of the pulse.

In particular embodiments, seed laser 400 may include a fiber laser. Asan example, seed laser 400 may include a fiber laser configured toproduce optical pulses, or seed laser 400 may include a CW fiber laser.As another example, seed laser 400 may include a wavelength-tunablefiber laser. As another example, seed laser 400 may include amode-locked fiber laser that produces optical pulses at a pulserepetition frequency greater than or equal to 1 MHz. Additionally, theseed laser 400 may include a pulse picker that extracts individualpulses from the optical pulses produced by the seed laser 400. The pulsepicker may include an electrically controlled electro-optic switch oracousto-optic modulator. As an example, a mode-locked fiber laser mayproduce optical pulses at a pulse repetition frequency of approximately100 MHz, and a pulse picker (which may be located after the fiber laser)may “pick” or extract one pulse out of every 100 pulses produced by thefiber laser, resulting in a pulse repetition frequency of approximately1 MHz. As another example, seed laser 400 may include a cavity-dumpedfiber laser. The fiber laser may include an optical switch (e.g., anacousto-optic modulator or a Pockels cell) located in the laser cavityand configured to periodically select or “dump” a pulse out of the lasercavity. For example, the seed laser 400 may be a mode-locked fiber laserwith a pulse repetition frequency of 75 MHz, and the cavity dumper mayselect 1 pulse out of every 100 pulses, resulting in an output pulserepetition frequency of approximately 750 kHz.

In particular embodiments, light source 110, laser 300, or seed laser400 may include a diode-pumped solid-state laser (DPSS laser). As anexample, seed laser 400 may include a Q-switched DPSS laser configuredto produce optical pulses in a free-space output beam 125 that iscoupled to scanner 120. A gain crystal of a DPSS laser may includeneodymium-doped yttrium aluminum garnet (Nd:YAG), neodymium-dopedyttrium aluminum borate (Nd:YAB), erbium-doped glass, or glass or YABdoped with erbium (e.g., Er:YAB) or doped with erbium and ytterbium(e.g., Er:Yb:YAB). The gain crystal may be pumped by a diode laser thatproduces a free-space pump beam coupled to the gain crystal. The pumplaser may operate at any suitable wavelength, such as for example,approximately 908 nm, 915 nm, 940 nm, 960 nm, 976 nm, 980 nm, 1050 nm,1064 nm, 1450 nm, or 1480 nm. A Q-switch of a DPSS laser may be anactive Q-switch (e.g., an acousto-optic modulator or electro-opticmodulator) or a passive Q-switch (e.g., a saturable-absorber material,such as for example, cobalt-doped spinel (MgAl₂O₄), glass doped withlead-sulfide (PbS) quantum dots, or vanadium-doped YAG).

FIG. 9 illustrates an example seed laser 400 that includes a laser diode440 and an optical modulator 460. In particular embodiments, seed laser400 may include a laser diode 440 configured to produce CW light and anamplitude modulator 460 configured to receive the CW light and produceoptical seed pulses from the received CW light. In particularembodiments, optical modulator 460 may be an electro-absorptionmodulator (EAM), an electro-optic modulator (EOM), a semiconductoroptical amplifier (SOA) modulator, or an acousto-optic modulator (AOM).An EAM may include a semiconductor material configured to modulate theintensity of light through a change in optical absorption caused by anapplied electric field. An EAM may be switched between a substantiallyabsorbing state and a substantially transmissive state to produceoptical pulses from CW light supplied by laser diode 440. An EOM mayinclude an electro-optic material (e.g., lithium niobate, lithiumtantalite, ammonium dihydrogen phosphate, potassium titanyl phosphate,potassium di-deuterium phosphate, β-barium borate, or a suitable organicpolymer) that exhibits the electro-optic effect in which the material'srefractive index changes in response to an applied electric field. As anexample, the EOM may be a fiber-coupled device that includes an opticalinterferometer formed by waveguides fabricated into a lithium-niobatesubstrate, where the optical transmission through the device ismodulated by changing the voltage applied across one arm of theinterferometer. A SOA may include a semiconductor gain medium that issubstantially opaque or absorbing when in an off state (e.g., whenlittle or no electrical current is applied to the SOA) and that istransparent or amplifying when current above a threshold current isapplied. By pulsing the current that drives the SOA, the SOA can produceoutput optical pulses from CW light supplied by laser diode 440. An AOMmay include a piezoelectric transducer attached to an optical material,and the piezoelectric material may be used to excite sound waves in theoptical material that diffract or deflect the direction of an opticalbeam.

In particular embodiments, modulator 460 may have an extinction ratio ofgreater than or equal to 10 dB, 20 dB, 30 dB, 40 dB, or any othersuitable value. The extinction ratio is an on/off ratio that representsthe amount of light transmitted through the modulator 460 in an on stateversus an off state. As an example, if modulator 460 transmits 10 μW ofaverage power in an on state and 10 nW of average power in an off state,then modulator 460 has an extinction ratio of 30 dB (which correspondsto 0.1% of optical leakage in the off state).

In particular embodiments, optical modulator 460 may be an externalmodulator coupled to laser diode 440 by optical fiber. As an example,optical modulator 460 may be a fiber-coupled EAM, EOM, or SOA configuredto receive CW light from laser diode 440 on an input optical fiber andproduce optical pulses on an output optical fiber. In particularembodiments, optical modulator 460 may be integrated into thesemiconductor structure of laser diode 440 or integrated into thepackaging of laser diode 440. As an example, laser diode 440 may have asemiconductor gain region configured to produce CW light, and the gainregion may be adjacent to a SOA or EA region that modulates the CWlight. In particular embodiments, laser diode 440 may be driven by a DCcurrent source (not illustrated in FIG. 9) to produce CW light, andmodulator 460 may be driven by a pulse generator 430 which in turn istriggered or driven by a function generator 420. In FIG. 9, functiongenerator 420 may produce voltage pulses, and pulse generator 430 maydrive the modulator 460 with voltage or current pulses that correspondto the pulses from the function generator 420. In particularembodiments, function generator 420 and pulse generator 430 may be twoseparate devices, or function generator 420 and pulse generator 430 maybe integrated together into a single device.

FIG. 10 illustrates an example seed laser 400 that includes a laserdiode 440 driven by a pulse generator 430A and an optical modulator 460driven by another pulse generator 430B. In particular embodiments, seedlaser 400 may include a laser diode 440 configured to producelonger-duration optical pulses (e.g., τ≅2-20 ns duration) and anamplitude modulator 460 configured to receive the longer-duration pulsesand produce shorter-duration seed pulses (e.g., Δt≅0.2-2 ns duration)from the received pulses. In the example of FIG. 10, laser diode 440produces optical pulses with a duration of τ, and modulator 460selectively transmits a portion of the laser-diode pulses to produceoutput optical seed pulses with a duration of Δt, where Δt<τ (e.g., τ≅5ns and Δt≅500 ps). In particular embodiments, the laser-diode pulses mayhave any suitable duration τ (e.g., 1 ns, 2 ns, 5 ns, 10 ns, or 20 ns),and the optical seed pulses may have any suitable duration Δt (e.g., 100ps, 200 ps, 400 ps, 600 ps, 1 ns, or 2 ns), where Δt<τ.

In FIG. 10, function generator 420 supplies voltage signals 422A and422B to pulse generators 430A and 430B, respectively. Function generator420 may supply a pulsed voltage signal 422A to pulse generator 430A, andpulse generator 430A may drive laser diode 440 with a correspondingpulsed current signal 432A. Function generator 420 may also supply apulsed voltage signal 422B to pulse generator 430B, and pulse generator430B may drive modulator 460 with a corresponding pulsed voltage orcurrent signal 432B. The pulsed signal 432A may include current pulseswith a duration of approximately T, and the pulsed signal 432B mayinclude current or voltage pulses with a duration of approximately Δt,where Δt<τ (e.g., τ≅5 ns and Δt≅500 ps). Additionally, a rising edge ofa pulse of signal 432B may be delayed by a delay time T with respect toa rising edge of a corresponding pulse of signal 432A. In particularembodiments, function generator 420 may be a single device with twooutputs, or function generator 420 may include two separate functiongenerators (e.g., a master function generator and a slave functiongenerator, where the output of the slave function generator is triggeredby or based on the output of the master). In particular embodiments,function generator 420 and pulse generators 430A and 430B may each beseparate devices, or two or three of these devices may be integratedtogether into a single device.

In particular embodiments, seed laser 400 may include a laser diode 440configured to produce optical pulses having a duration τ. The seed laser400 may also include an optical modulator 460 configured to receive theoptical pulses from the laser diode 440 and selectively transmit aportion of each of the received optical pulses to produce output opticalseed pulses, where each optical seed pulse has a duration less than τ.In FIG. 10, the laser diode 440 produces an optical pulse with aduration τ, and the modulator selects a portion of the laser-diode pulseto produce a seed pulse with a duration of Δt, where Δt<τ. The selectedportion of the laser-diode pulse may be delayed by delay T with respectto the rising edge of the laser-diode pulse. In FIG. 10, the selectedportion of the laser-diode pulse includes the portion of the laser-diodepulse between the two vertical dashed lines having a Δt separation,where one line is delayed by delay T with respect to the rising edge ofthe laser-diode pulse. As an example, the laser-diode pulse may have aduration τ of 5 ns, and the seed pulse may have a duration Δt of 0.5 ns.If the delay time T is 2 ns, then modulator 460 may transmit the portionof the laser-diode pulse from approximately 2 ns to 2.5 ns after therising edge of the laser-diode pulse.

As illustrated in FIG. 10, an optical pulse emitted by laser diode 440may include one or more initial spikes or oscillations in intensityfollowed by a plateau region with a substantially uniform intensity. Inparticular embodiments, modulator 460 may transmit a portion of aplateau region of the laser-diode pulse, resulting in an emitted seedpulse that may be substantially uniform or stable (e.g., the seed pulsemay exhibit little or no intensity spikes or oscillations).Additionally, the seed pulse may exhibit little or no substantialwavelength variation relative to the initial portion of the laser-diodepulse. The modulator 460 is driven to select a slice or portion of thelaser-diode pulse by switching from an off state (or, absorptive state)to an on state (or, transmissive state) for a duration of time Δt. Inparticular embodiments, since laser diode 440 is operating in a pulsedmode (rather than a CW mode), the output seed pulses may exhibit littleor no presence of leakage light during the time between successive seedpulses.

In particular embodiments, the modulator 460 may be driven in a digitalfashion between on and off states. As an example, the modulator 460 maybe driven from an absorbing state to a transmitting state and then backto an absorbing state, which may result in a seed pulse with asubstantially square shape (as illustrated in the example of FIG. 10).In particular embodiments, the modulator 460 may be driven in an analogfashion to produce seed pulses with other suitable shapes, such as forexample, triangular, Gaussian, or arbitrary shapes. As an example, themodulator 460 may be driven relatively gradually from an absorbing stateto a transmitting state to produce a seed pulse with a gradually risingfront edge. Similarly, the modulator 460 may be driven relativelygradually from a transmitting state to an absorbing state to produce aseed pulse with a gradually falling trailing edge.

FIG. 11 illustrates an example seed laser 400 with multiple laser diodes(440-1, 440-2, . . . , 440-N) that are combined together by amultiplexer 412. In particular embodiments, seed laser 400 may includemultiple laser diodes 440 configured to operate at multiple differentwavelengths and an optical multiplexer 412 configured to combine thelight produced by each laser diode 440 into a single output opticalfiber. As an example, seed laser 400 may include N laser diodes 440configured to operate at N different wavelengths. In particularembodiments, each laser diode 440 may be a pulsed laser diode driven bya separate pulse generator 430 (not illustrated in FIG. 10). As anexample, N separate pulse generators 430 may each be driven or triggeredby a separate function generator 420 (not illustrated in FIG. 10). Thefunction generators 420 may operate independently or may be synchronizedwith respect to one another so that the pulses can be emitted with aparticular time delay between successive pulses. As another example, theN pulse generators 430 may be driven by a single function generator 420that has N trigger-signal outputs. Additionally, the function generator420 may have N−1 electrical delays so that the pulses from each laserdiode 440 can be synchronized or time-delayed with respect to oneanother. In particular embodiments, any suitable number of functiongenerators 420, pulse generators 430, or electrical delays may beintegrated together into a single device.

In particular embodiments, multiplexer 412 may be referred to as awavelength combiner, a mux, or a wavelength division multiplexer (WDM).In particular embodiments, multiplexer 412 may be similar todemultiplexer 410 described above, where the direction of light inmultiplexer 412 is reversed with respect to demultiplexer 410. As anexample, multiplexer 412 may have N input ports coupled to N laserdiodes 440, and multiplexer 412 may combine light from the input portstogether into a single output port. In particular embodiments, a N×1multiplexer 412 may perform wavelength combining using a prism,diffraction grating, holographic grating, arrayed waveguide grating, orone or more dichroic filters. In particular embodiments, seed laser 400may include N optical amplifiers (not illustrated in FIG. 10). As anexample, each laser diode 440 may be coupled to an optical amplifierlocated between the laser diode and the multiplexer 412. The opticalamplifiers may be configured to amplify the light from each laser diode440 separately prior to combining in multiplexer 412.

In particular embodiments, the N laser diodes 440 may produce opticalpulses at N respective wavelengths, and each laser diode 440 may producepulses at a pulse repetition frequency f. Additionally, the pulsesproduced by each of the laser diodes 440 may be synchronized so thatafter being combined together by multiplexer 412 the output seed pulsesinclude N sets of time-interleaved pulses which are substantially evenlyspaced in time. As an example, each laser diode 440 may emit pulses thatare delayed with respect to pulses from a preceding laser diode 440 by atime delay of 1/(f×N). The pulses from the N laser diodes 440 may becombined by the N×1 multiplexer 412, resulting in an output seed-laserrepetition frequency of f×N. As an example, seed laser 400 may includeN=8 laser diodes 440, and each laser diode 440 may produce pulses at af=640-kHz pulse repetition frequency with a time delay relative topulses emitted by a preceding laser diode 440 of 1/(640 kHz×8)≅195 ns.This results in an output seed-laser repetition frequency ofapproximately 5.12 MHz with a pulse period of approximately 195 ns. Inparticular embodiments, the output seed-laser pulses may be sent to afiber-optic amplifier for amplification. A fiber-optic amplifier mayexhibit improved performance (e.g., reduced amplified spontaneousemission) when amplifying the output seed-laser pulses due to the higherpulse repetition frequency and higher duty cycle provided by combiningpulses from multiple laser diodes 440 into a single pulse stream foramplification. Additionally, undesirable nonlinear effects in opticalfiber may be reduced or avoided by interleaving the pulses in atime-synchronized manner so that the pulses do not overlap in time.

FIG. 12 illustrates an example wavelength-dependent delay line 500. Inparticular embodiments, a lidar system 100 may include awavelength-dependent delay line 500 configured to receive input lightthat includes the N operating wavelengths of the lidar system 100 andproduce time-delayed output light. The delay line 500 imparts awavelength-dependent time delay so that the time-delayed output lightincludes the input light where each wavelength of input lightexperiences a particular time delay based on its wavelength. In theexample of FIG. 12, the delay line 500 includes an optical circulator510, N fiber Bragg gratings (FBGs) 520, and N−1 fiber delays 530. Inparticular embodiments, circulator 510 may be a three-port fiber-opticcomponent that directs light that enters at one port out to anotherport. In FIG. 12, light entering at port 1 (the input of delay line 500)is directed to port 2, and light entering at port 2 is directed to port3 (the output of delay line 500).

In particular embodiments, a FBG 520 may be a fiber-optic component thatincludes a periodic variation in the refractive index of the fiber core(e.g., a distributed Bragg reflector, an apodized grating, or a chirpedfiber Bragg grating) which acts as a wavelength-specific reflector. EachFBG 520 corresponds to a particular operating wavelength of the lidarsystem 100 and is configured to reflect that particular operatingwavelength and transmit the other wavelengths of the lidar system 100.As an example, laser 300 or seed laser 400 may produce optical pulses atN different wavelengths (e.g., wavelengths λ₁, λ₂, . . . , λ_(N)), anddelay line 500 may include N FBGs 520 corresponding to each of the Nwavelengths. FIG. 12 includes example reflection spectra for each of theFBGs 520 where the x-axis corresponds to wavelength and the y-axiscorresponds to reflected optical power (P_(R)). FBG-λ1 reflects light atwavelength λ1 (over a Δλ bandwidth) and transmits light at otherwavelengths. Similarly, FBG-λ2, FBG-λ3, and FBG-XN each reflect light atwavelengths λ2, λ3, and λN, respectively. Each FBG 520 may have anysuitable reflectively (e.g., reflectivity greater than or equal to 50%,75%, 90%, 95%, 99%, or 99.9%) over any suitable bandwidth (e.g., Δλ maybe approximately 0.1 nm, 0.2 nm, 0.5 nm, 1 nm, 5 nm, 10 nm, or 20 nm).As an example, FBG-λ1 may have a reflectivity of greater than 99% over a0.5-nm bandwidth centered at 1550.1 nm.

In particular embodiments, delay line 500 may include multiple FBGs 520arranged in series and separated from one another by a fiber delay 530,where fiber delay 530 is a particular length of optical fibercorresponding to a particular round-trip delay time ΔT. The length L offiber delay 530 may be related to a time delay ΔT between pulsesreflected by successive FBGs 520 based on the expression 2·L=ΔT·c/n,where n is the refractive index experienced by light traveling throughthe fiber delay 530. As an example, a time delay of approximately 195 nscan be achieved with an optical fiber having a refractive index of 1.44and a length of 20.3 m. In FIG. 12, light with wavelength λ1 isreflected by FBG-λ1 and proceeds to the output of delay line 500. Lightwith wavelength λ2 passes through FBG-λ1, is reflected by FBG-λ2, andthen proceeds to the output with a time delay (relative to theλ1-wavelength light) of approximately ΔT. Light with wavelength λ3passes through FBG-λ1 and FBG-λ2, is reflected by FBG-λ3, and thenproceeds to the output with a time delay (relative to the λ1-wavelengthlight) of approximately 2·ΔT. Light with wavelength λN passes throughthe first N−1 FBGs, is reflected by FBG-λN, and then proceeds to theoutput with a time delay (relative to the λ1-wavelength light) ofapproximately (N−1)·ΔT. Any light that falls outside the reflectionbands of the N FBGs 520 may pass through the FBGs 520. This outside-bandlight (which may include undesirable noise or amplified spontaneousemission from an optical amplifier) may be prevented from propagatingthrough the delay line 500 and effectively filtered out from the lidarsystem 100.

In particular embodiments, a wavelength-dependent delay line 500 may beincluded in a seed laser 400 or an optical amplifier, or awavelength-dependent delay line 500 may be located between a seed laser400 and an optical amplifier or between two optical amplifiers. Inparticular embodiments, a wavelength-dependent delay line 500 may beused in a lidar system 100 to separate one broadband pulse of light intoN time-delayed pulses of light. As an example, a seed laser 400 (or aseed laser 400 followed by an optical amplifier) may be configured toproduce broadband pulses of light with a spectral bandwidth that coversthe N operating wavelengths of a lidar system 100. As an example, alidar system 100 may operate with N=8 wavelengths of light (e.g.,wavelengths λ₁, λ₂, . . . , λ₈), and each pulse produced by seed laser400 may have an optical spectrum that includes or spans the 8wavelengths. The seed-laser pulses may be sent to the input of delayline 500, which may produce 8 pulses at the output, where each of the 8pulses corresponds to one of the 8 lidar-system operating wavelengths.The 8 pulses may be time delayed with respect to one another accordingto the length of the respective fiber delays 530. As an example, delayline 500 may receive broadband input pulses with a pulse repetitionfrequency f, and the output pulses may have a pulse repetition frequencyof f×N and a time delay ΔT between successive output pulses ofapproximately 1/(f×N). In particular embodiments, each fiber delay 530may have approximately the same length so that successive output pulseshave substantially the same time delay with respect to one another. Inparticular embodiments, undesirable nonlinear effects in optical fibermay be reduced or avoided by separating a broadband input pulse intomultiple output pulses, since the multiple output pulses are separatedin time and have reduced peak powers compared to the input pulse.

In particular embodiments, a wavelength-dependent delay line 500 may beused in a lidar system 100 to separate N time-coincident pulses of lightinto N time-delayed pulses of light. As an example, seed laser 400 mayinclude N laser diodes 400 configured to produce pulses at N differentwavelengths with little or no substantial time delay between the pulses.The seed-laser pulses may be triggered by a signal from a single-outputfunction generator 420 so that the pulses are emitted at substantiallythe same time. The N time-coincident pulses may be passed through adelay line 500 to produce N pulses separated from one another by aparticular time delay according to wavelength.

FIG. 13 illustrates an example lidar system 100 that includes a seedlaser 400, amplifier 470, and sensor 310. In particular embodiments, alidar system 100 may include one or more seed lasers 400, one or moreamplifiers 470, or one or more sensors 310. In particular embodiments,seed laser 400 may include (1) a laser diode (e.g., a DFB laser) drivenby a pulse generator 430, (2) a wavelength-tunable laser configured toproduce light at multiple wavelengths, (3) multiple laser diodes 440configured to produce light at multiple respective wavelengths, or (4)any other suitable laser source. In particular embodiments, seed laser400 may produce low-power optical pulses, and one or more opticalamplifiers 470 may be configured to amplify the low-power pulses toproduce amplified pulses of light. The amplified pulses of light maycorrespond to optical pulses emitted by laser 300. As an example,amplifier 470 may receive optical seed pulses having an average power ofgreater than or equal to 1 microwatt, and the amplified output pulsesfrom the amplifier 470 may have an average power of greater than orequal to 1 mW. As another example, amplifier 470 may receive opticalseed pulses having a pulse energy of greater than or equal to 1 pJ, andthe amplified output pulses from the amplifier 470 may have a pulseenergy of greater than or equal to 0.1 μJ.

In particular embodiments, an amplifier 470 may be referred to as afiber amplifier, optical amplifier, fiber-optic amplifier, optical amp,or amp. In particular embodiments, all or part of an amplifier 470 maybe included in a laser 300, an optical link 330, or a sensor head 310.In particular embodiments, an amplifier 470 may include any suitablenumber of optical-amplification stages. As an example, an amplifier 470of a lidar system 100 may include 1, 2, 3, 4, or 5 optical-amplificationstages. In particular embodiments, amplifier 470 may include asingle-pass amplifier in which light makes one pass through theamplifier 470. In particular embodiments, amplifier 470 may include adouble-pass amplifier in which light makes two passes through theamplifier gain medium. In particular embodiments, amplifier 470 may actas a preamplifier (e.g., an amplifier that amplifies seed pulses from alaser diode 440 or a seed laser 400), a mid-stage amplifier (e.g., anamplifier that amplifies light from another amplifier), or a boosteramplifier (e.g., an amplifier that sends output light to a scanner 120or a sensor head 310). A preamplifier may refer to the first amplifierin a series of two or more amplifiers, a booster amplifier may refer tothe last amplifier in a series of amplifiers, or a mid-stage amplifiermay refer to any amplifier located between a preamplifier and a boosteramplifier.

In particular embodiments, amplifier 470 may provide any suitable amountof optical power gain, such as for example, a gain of approximately 5dB, 10 dB, 20 dB, 30 dB, 40 dB, 50 dB, 60 dB, or 70 dB. As an example,amplifier 470 (which may include two or more separate amplificationstages) may receive pulses with a 1-μW average power and produceamplified pulses with a 5-W average power, corresponding to an opticalpower gain of approximately 67 dB. As another example, amplifier 470 mayinclude two or more amplification stages each having a gain of greaterthan or equal to 20 dB, corresponding to an overall gain of greater thanor equal to 40 dB. As another example, amplifier may include threeamplification stages having gains of approximately 30 dB, 20 dB, and 10dB, respectively, corresponding to an overall gain of approximately 60dB.

FIG. 14 illustrates an example spectrum of an optical signal before andafter passing through a spectral filter. In particular embodiments, aspectral filter, which may be referred to as an optical filter, mayinclude an absorptive filter, dichroic filter, long-pass filter,short-pass filter, or band-pass filter. In particular embodiments, aspectral filter may be substantially transmissive to light over aparticular range of wavelengths (e.g., a pass-band) and maysubstantially block (e.g., through absorption or reflection) thetransmission of light outside of the pass-band range. As an example, aspectral filter may be a dichroic filter (which may be referred to as areflective, thin-film, or interference filter) which includes asubstantially transparent optical substrate (e.g., glass or fusedsilica) with a series of thin-film optical coatings configured totransmit light over a particular wavelength range and reflect otherwavelengths of light. As another example, a spectral filter may includea FBG 520 configured to transmit light over a particular pass-band andsubstantially block light outside of the pass-band. In the example ofFIG. 14, the spectral filter is a band-pass filter with a centerwavelength of λ_(C) and a pass-band from λ_(LO) to λ_(III), whichcorresponds to a filter bandwidth of λ_(HI)-λ_(LO).

In particular embodiments, a spectral filter may have an opticaltransmission (within a pass-band) of greater than or equal to 50%, 70%,80%, 90%, 95%, 99%, or any other suitable transmission value.Additionally, a spectral filter may have an optical transmission of lessthan or equal to 50%, 20%, 10%, 1%, 0.5%, 0.1%, or any other suitabletransmission value for wavelengths outside the pass-band. The opticaltransmission outside the pass-band may also be expressed in terms ofdecibels (dB) of attenuation. For example, the filter attenuation forwavelengths outside the pass-band may be greater than or equal to 3 dB,10 dB, 15 dB, 20 dB, 30 dB, or any other suitable attenuation value. Anattenuation value of 20 dB corresponds to blocking approximately 99% ofthe incident light power and transmission of approximately 1% ofincident light. In particular embodiments, a spectral filter maytransmit light at one or more operating wavelengths of a lidar system100 and block or attenuate light away from the transmitted wavelengthsby greater than or equal to 3 dB, 10 dB, 15 dB, 20 dB, 30 dB, or anyother suitable attenuation value. The light that is away from thetransmitted wavelengths may refer to light with a wavelength outside ofa pass-band of the spectral filter. As an example, a spectral filter maytransmit greater than or equal to 90% of incident light within aspectra-filter pass-band and may block or attenuate light outside of thepass-band by 20 dB. As another example, a spectral filter may have afilter attenuation of greater than or equal to 20 dB for wavelengthsbetween approximately [λ_(LO)-100 nm] and λ_(LO) and wavelengths betweenapproximately λ_(HI) and [+100 nm].

In particular embodiments, a spectral filter may have any suitablefilter bandwidth, such as for example, a filter bandwidth of 0.1 nm, 0.2nm, 0.5 nm, 1 nm, 2 nm, 5 nm, or 10 nm. As an example, a spectral filtermay have a pass-band with a 1-nm bandwidth that is centered about centerwavelength 1554.9 nm. In particular embodiments, an optical filter mayhave a relatively narrow pass-band (e.g., a spectral-filter bandwidth ofless than or equal to 0.05 nm, 0.1 nm, 0.2 nm, 0.5 nm, or 1 nm), and alaser diode 440 of the lidar system 100 may be temperature stabilized sothat the laser-diode operating wavelength is matched to thespectral-filter pass-band. In particular embodiments, an optical filtermay have a relatively broad pass-band (e.g., a spectral-filter bandwidthof greater than or equal to 1 nm, 2 nm, 5 nm, 10 nm, 20 nm, or 50 nm),and a laser diode 440 may not require temperature stabilization tomaintain its operating wavelength within the spectral-filter pass-band.

In particular embodiments, an optical spectrum before passing through aspectral filter may include a signal spectrum along with backgroundoptical noise, which may include amplified spontaneous emission (ASE)originating from an amplifier 470. In FIG. 14, the signal spectrum,which may represent the spectrum for a series of optical pulses, iscentered at wavelength λ_(C) and has a bandwidth of δλ. The signalspectrum is contained within the pass-band of the spectral filter andpasses through the filter with little or no attenuation (e.g., ≦10%attenuation). Similarly, the optical pulses associated with the signalspectrum may pass through the filter with little or no attenuation ordistortion to their shape. In FIG. 14, the optical spectrum beforepassing through the spectral filter includes a broadband offsetassociated with ASE. In particular embodiments, an ASE spectrum mayextend over a wavelength range of approximately 20 nm, 40 nm, 60 nm, or80 nm (e.g., from approximately 1510 nm to approximately 1590 nm). Theportion of the ASE that falls outside the spectral-filter pass-band maybe substantially attenuated, as indicated by the after-spectral-filterspectrum illustrated in FIG. 14 where wavelengths less than λ_(LO) andgreater than λ_(HI) are attenuated after passing through the spectralfilter. In particular embodiments, a spectral filter may be used toreduce or substantially remove unwanted optical signals or noise (e.g.,ASE) from a laser 300, seed laser 400, or amplifier 470 of a lidarsystem 100. As an example, an optical filter may be located at or nearan output of an optical amplifier 470, and the filter may be configuredto remove any suitable amount of the ASE from the amplifier output 470,such as for example, 50%, 60%, 80%, 90%, 95%, or 99% of the ASE. Asanother example, an optical filter with a 1-nm bandwidth that receives asignal with background optical noise that extends over approximately 50nm may remove approximately 94% to 98% of the background noise from thesignal.

In particular embodiments, a spectral filter may have a single pass-band(e.g., 1550-1552 nm) or two or more distinct pass-bands (e.g., 1550-1552nm and 1555-1557 nm). As an example, for a lidar system 100 with Noperating wavelengths, a spectral filter may have N pass-bandscorresponding to each of the N operating wavelengths. In particularembodiments, the center wavelength λ_(C) or the bandwidth δλ of aspectral filter may be substantially fixed. In particular embodiments, aspectral filter may have an adjustable center wavelength λ_(C) or anadjustable bandwidth δλ. As an example, the center wavelength of aspectral filter may be dynamically changed to match the changingwavelength of a wavelength-tunable seed laser 400 or laser diode 440.

FIG. 15 illustrates example optical pulses before and after the pulsespass through a temporal filter. In particular embodiments, opticalpulses from a laser diode 440, seed laser 400, laser 300, or amplifier470 may be passed through a temporal filter to reduce or removeinter-pulse noise (e.g., optical noise located temporally betweensuccessive pulses). In particular embodiments, a temporal filter mayhave a transmitting state (which may be referred to as an “on” or “open”state) and a non-transmitting state (which may be referred to as an“off” or “closed” state). A temporal filter in the transmitting statemay be substantially transmissive or may allow light to propagatethrough the filter with minimal attenuation (e.g., the filter may havean optical transmission of greater than or equal to 70%, 80%, 90%, 95%,or 99%). In the non-transmitting state, the filter may be substantiallyopaque or blocking (e.g., the filter may have an optical transmissionless than or equal to 20%, 10%, 2%, 1%, 0.5%, or 0.1%). As an example,when a temporal filter is in a non-transmitting state, an optical signal(e.g., ASE) may be substantially prevented from being transmittedthrough the filter (e.g., the optical signal may experience anattenuation of greater than or equal to 10 dB, 20 dB, 30 dB, 40 dB, orany other suitable attenuation value).

In particular embodiments, a temporal filter may be configured to be ina transmitting state when an optical pulse is present and to be in anon-transmitting state otherwise. As an example, an optical amplifier470 may receive and amplify pulses from a seed laser 400, and a temporalfilter located at the output of the amplifier 470 may be switchedbetween transmitting and non-transmitting states according to when anamplified seed pulse is present. The temporal filter may receive atrigger signal from seed laser 400 or function generator 420 indicatingwhen the filter should switch from non-transmitting to transmitting orfrom transmitting to non-transmitting. In the example of FIG. 15, thepulses before passing through a temporal filter have a pulse width of Δtand an amount of ASE offset noise (e.g., ASE produced by an amplifier470). After passing through the temporal filter, the pulses retain theirduration and overall shape, and the amount of ASE noise betweensuccessive pulses is reduced. When a pulse is present (e.g., when apulse is incident on or traveling through the temporal filter), thefilter is in the open state, and when there is no pulse present, thefilter switches to the closed state. In particular embodiments, atemporal filter may be configured to be open for a duration of time thatis greater than or equal to the pulse duration Δt. As an example, atemporal filter may be configured to be open for a period of timeapproximately equal to Δt, 2Δt, 3Δt, 5Δt, or 10Δt. As another example, atemporal filter may be open for a 2Δt window of time, where the windowis approximately centered on the time when the pulse is present.

In particular embodiments, a temporal filter, which may be referred toas an optical filter, may include an optical switch, a SOA device, or anelectro-absorption (EA) device. As an example, a temporal filter mayinclude an on/off optical switch that employs any suitable switchingmechanism (e.g., mechanical switching, piezoelectric switching, thermalswitching, liquid-crystal switching, switching with a MEMS device, orswitching between waveguides in a PLC) to selectively switch betweenallowing light to pass through the switch and blocking or preventinglight from being transmitted through the switch. As another example, atemporal filter may include a SOA device that is substantially opaque orabsorbing when in a non-transmitting state (e.g., when little or noelectrical current is applied to the SOA device) and that is transparentor amplifying when current above a threshold current is applied. Asanother example, a temporal filter may include an EA device that blocksor transmits light through a change in optical absorption caused by anelectric field applied to a semiconductor material.

In particular embodiments, an optical filter may include a spectralfilter, a temporal filter, or a combination of a spectral filter and atemporal filter. As an example, an optical filter may include a seriescombination of a spectral filter and a temporal filter (e.g., a spectralfilter followed by a temporal filter, or vice versa). In particularembodiments, lidar system 100 may include one or more spectral filtersor one or more temporal filters. As an example, one or more spectral ortemporal filters may be included in laser 300, sensor 310, optical link330, seed laser 400, or amplifier 470. As another example, one or moreoptical filters may be located at an input or output of an amplifier470. In particular embodiments, a lidar system 100 may include one ormore optical filters, where each optical filter is configured to reducean amount of ASE light produced by one or more optical amplifiers 470.As an example, one or more optical filters may be located at the outputof an amplifier 470 to reduce the amount of ASE from the amplifier 470that propagates beyond the amplifier 470. In particular embodiments, alidar system 100 may include an optical amplifier 470 that includes oneor more optical filters, where each optical filter is configured toreduce an amount of ASE light produced by the optical amplifier 470. Inparticular embodiments, a lidar system 100 that includes one or moreoptical filters may exhibit a reduced amount of optical or electricalnoise relative to a lidar system without optical filters. In particularembodiments, a laser system or amplifier 470 that includes one or moreoptical filters or optical isolators may be substantially prevented fromproducing unwanted light (e.g., through Q-switching or self lasing) whenno optical pulse is present. As an example, during a time betweensuccessive optical pulses, one or more optical filters or isolators mayprevent an amplifier 470 from emitting a Q-switched pulse.

FIG. 16 illustrates an example double-pass fiber-optic amplifier 470. Inparticular embodiments, an optical amplifier 470 may receive light atits input, amplify the input light, and send the amplified light to anoutput. The received input light may include optical pulses from a seedlaser 400 or from a previous amplification state (e.g., two or moreamplifiers 470 may be coupled together in series). The amplified outputlight may be sent to another amplifier 470 (e.g., to provide anotherstage of amplification), a demultiplexer 410 (e.g., for distribution tomultiple optical links 330 or multiple sensor heads 310), an opticallink 330, or a sensor head 310. In particular embodiments, an amplifier470 may be part of a master oscillator power amplifier (MOPA) or masteroscillator fiber amplifier (MOFA) in which a master oscillator (e.g., aseed laser 400) sends relatively low-power optical pulses to one or moreoptical amplifiers 470 for amplification. As an example, an amplifier470 may receive pulses with an input pulse energy (E_(in)) ofapproximately 10 pJ and produce amplified pulses with an output pulseenergy (E_(out)) of approximately 10 nJ. The optical gain (G) of theamplifier 470 in decibels, which may be determined from the expressionG=10 log(E_(out)/E_(in)), is approximately 30 dB. As another example, anamplifier 470 may receive input pulses with a peak power (P_(in)) ofapproximately 10 W and produce amplified output pulses with a peak power(P_(out)) of approximately 1 kW. The optical gain (G) of the amplifier470, which may be determined from the expression G=10log(P_(out)/P_(in)), is approximately 20 dB.

In particular embodiments, an optical amplifier 470 may include one ormore circulators 510, one or more couplers (600A, 600B), one or morephotodiodes (PD 610A, PD 610B), one or more isolators (620A, 620B), oneor more filters 630, one or more pump lasers 640, one or more pump WDMs650, one or more gain fibers 660, or one or more reflectors 670. Thedouble-pass amplifier 470 illustrated in FIG. 16 includes an inputcoupler 600A and photodiode (PD) 610A, an input isolator 620A, acirculator 510, a pump laser 640 and pump WDM 650, a gain fiber 660, areflector 670, an output isolator 620B, an output coupler 600B and PD610B, and an output filter 630. In the example of FIG. 16, after passingthrough the coupler 600A and isolator 620A, the input light is directedfrom port 1 to port 2 of circulator 510 and then travels through pumpWDM 650 and gain fiber 660. The light is reflected by reflector 670 andtravels back through gain fiber 660 and pump WDM 650. During the twopasses through the gain fiber 660, the input light undergoesamplification through a process of stimulated emission. The amplifiedlight is directed from port 2 to port 3 of the circulator where it thentravels through isolator 620B, coupler 600B, and filter 630. Theamplified light is directed to the output of amplifier 470, at whichpoint the amplified output light may be sent to another amplifier 470, ademultiplexer, an optical link 330, or a sensor head 310.

In particular embodiments, a fiber-optic amplifier 470 may include again fiber 660 that is optically pumped (e.g., provided with energy) bya pump laser 640. The optically pumped gain fiber 660 provides opticalgain to particular wavelengths of light traveling through the gain fiber660. The pump light and the light to be amplified may both propagatesubstantially through the core of the gain fiber 660. The gain fiber 660may be an optical fiber doped with rare-earth ions, such as for exampleerbium (Er), neodymium (Nd), ytterbium (Yb), praseodymium (Pr), holmium(Ho), thulium (Tm), dysprosium (Dy), any other suitable rare-earthelement, or any suitable combination thereof. The rare-earth dopantsabsorb light from the pump laser 640 and are “pumped” or promoted intoexcited states that provide amplification to particular wavelengths oflight through stimulated emission. The rare-earth ions in excited statesmay also emit photons through spontaneous emission, resulting in theproduction of ASE light by amplifier 470. In particular embodiments, anamplifier 470 with erbium-doped gain fiber 660 may be referred to as anerbium-doped fiber amplifier (EDFA) and may be used to amplify lighthaving wavelengths between approximately 1520 nm and approximately 1600nm. In particular embodiments, a gain fiber 660 may be doped with acombination of erbium and ytterbium dopants and may be referred to as aEr:Yb co-doped fiber, Er:Yb:glass fiber, Er:Yb fiber, Er:Yb-doped fiber,or erbium/ytterbium-doped fiber. An amplifier 470 with Er:Yb co-dopedgain fiber may be referred to as an erbium/ytterbium-doped fiberamplifier (EYDFA). An EYDFA may be used to amplify light havingwavelengths between approximately 1520 nm and approximately 1620 nm. Inparticular embodiments, a gain fiber 660 doped with ytterbium may bepart of a ytterbium-doped fiber amplifier (YDFA). A YDFA may be used toamplify light having wavelengths between approximately 1000 nm andapproximately 1130 nm. In particular embodiments, a gain fiber 660 dopedwith thulium may be part of a thulium-doped fiber amplifier (TDFA). ATDFA may be used to amplify light having wavelengths betweenapproximately 1900 nm and approximately 2100 nm.

In particular embodiments, a fiber-optic amplifier 470 may refer to anamplifier where light is amplified while propagating through a gainfiber 660 (e.g., the light is not amplified while propagating as afree-space beam). In particular embodiments, an amplifier 470 where thelight being amplified makes one pass through a gain fiber 660 may bereferred to as a single-pass amplifier 470 (as described below), and anamplifier 470 where the light being amplified makes two passes through again fiber 660 (as illustrated in FIG. 16) may be referred to as adouble-pass amplifier 470. In particular embodiments, the length of gainfiber 660 in an amplifier 470 may be 0.5 m, 1 m, 2 m, 4 m, 6 m, 10 m, 20m, or any other suitable gain-fiber length. In particular embodiments,gain fiber 660 may be a SM or LMA optical fiber with a core diameter ofapproximately 7 μm, 8 μm, 9 μm, 10 μm, 12 μm, 20 μm, 25 μm, or any othersuitable core diameter. The numerical aperture (NA), composition, orrefractive indices of the components of an optical fiber may beconfigured so that the optical fiber remains in single-mode operationfor the wavelength of light propagating through the fiber. In theexample of FIG. 16 (as well as some of the other figures describedherein), a line or an arrow between two optical components may representa fiber-optic cable. As an example, coupler 600A and isolator 620A maybe coupled together by a fiber-optic cable represented by the arrow thatconnects the two components. As another example, the input and outputillustrated in FIG. 16 may each represent a fiber-optic cable.

In particular embodiments, pump laser 640 may produce light at anywavelength suitable to provide optical excitation to the dopants of gainfiber 660. As an example, pump laser 640 may be a fiber-coupled laserdiode with an operating wavelength of approximately 908 nm, 915 nm, 940nm, 960 nm, 976 nm, 980 nm, 1050 nm, 1064 nm, 1450 nm, or 1480 nm. Asanother example, an erbium-doped or erbium/ytterbium-doped gain fiber660 may be pumped with a 976-nm laser diode. In particular embodiments,pump laser 640 may be operated as a CW light source and may produce anysuitable amount of average optical pump power, such as for example,approximately 100 mW, 500 mW, 1 W, 2 W, 5 W, or 10 W of pump power. Inparticular embodiments, light from pump laser 640 may be coupled intogain fiber 660 via a pump wavelength-division-multiplexer (WDM) 650. Apump WDM 650 may refer to a three-port device that combinesinput-amplifier light at port 1 having a particular wavelength with pumplight at port 2 having a different wavelength and sends the combinedlight out port 3. As an example, the input-amplifier light may have awavelength of approximately 1530-1565 nm and may be combined by pump WDM650 with pump-laser light having a wavelength of approximately 975-985nm. The combined light is then coupled to gain fiber 660, where thepump-laser light pumps the gain fiber 660, and the input-amplifier lightis amplified. The input-amplifier light makes a first pass through thegain fiber, is reflected by reflector 670, and then makes a second passthrough the gain fiber 660. The amplified light then passes through pumpWDM 650 and back to port 2 of the circulator 510 where it is sent toport 3.

In particular embodiments, reflector 670 may include a mirror or a FBG520. As an example, reflector 670 may include a metallic or dielectricmirror configured to receive light from gain fiber 660 and reflect thereceived light back into the gain fiber 660. As another example,reflector 670 may include one or more FBGs 520 configured to reflectlight corresponding to one or more operating wavelengths of lidar system100 and transmit or attenuate light that is away from the reflectedwavelengths. For example, reflector 670 may include a FBG 520 thatreflects light between approximately 1400 nm to approximately 1440 nmand transmits light over the wavelength ranges of approximately1300-1400 nm and approximately 1440-1540 nm. In particular embodiments,a double-pass amplifier 470 may include a circulator 510, a gain fiber660 having a first end and a second end, and a FBG 520, where the firstend of the gain fiber 660 is coupled to the circulator 510 and thesecond end is coupled to the FBG 520. In FIG. 16, the upper end of gainfiber 660 is coupled to port 2 of circulator 510 via pump WDM 650, andthe lower end of gain fiber 660 is coupled to reflector 670, which mayinclude one or more FBGs 520.

In particular embodiments, reflector 670 may include a FBG 520 thatreflects light at the wavelength of the input light that is received andamplified by amplifier 470. As an example, amplifier 470 may receivepulses of light having a wavelength of approximately 1552 nm, andreflector 670 may include a FBG 520 configured to reflect light at 1552nm. The FBG 520 may be similar to the FBGs 520 described above withrespect to FIG. 12. The FBG 520 may have any suitable reflectively(e.g., reflectivity greater than or equal to 50%, 75%, 90%, 95%, 99%, or99.9%) over any suitable bandwidth (e.g., Δλ may be approximately 0.1nm, 0.2 nm, 0.5 nm, 1 nm, 5 nm, 10 nm, or 20 nm). As an example,reflector 670 may include a FBG 520 with a reflectivity of greater thanor equal to 99% over a 2-nm bandwidth centered at 1552 nm. As anotherexample, reflector 670 may include a FBG 520 with a reflectivity ofgreater than or equal to 90% over a 10-nm bandwidth centered at 1550 nm.In particular embodiments, a reflector 670 may include a FBG 520 with arelatively narrow reflectivity range (e.g., the bandwidth Δλ may be lessthan or equal to 0.1 nm, 0.2 nm, 0.5 nm, 1 nm, or 2 nm), and lidarsystem 100 may include a laser diode 440 that is temperature stabilizedso that its operating wavelength matches the reflectivity range of theFBG 520.

In particular embodiments, reflector 670 may include a FBG 520 thatreflects light at one or more operating wavelengths and transmits orattenuates light that is away from the one or more operatingwavelengths. As an example, the FBG 520 may reflect light fromapproximately 1555 nm to approximately 1560 nm, and the FBG 520 maytransmit light at wavelengths outside that range. In particularembodiments, outside of its range of reflectivity, a FBG 520 may have areflectivity of less than or equal to 50%, 20%, 10%, 5%, 2%, 1%, 0.5%,or less than any suitable reflectivity value. As an example, a FBG 520with a reflectivity range of 1555-1560 nm may have a reflectivity ofless than or equal to 50% (or, a transmission of greater than or equalto 50%) over the ranges of approximately 1455-1555 nm and approximately1560-1660 nm. In particular embodiments, out-of-band light (e.g., lightthat is outside the reflectivity range of a FBG 520) may besubstantially transmitted through the FBG 520. In FIG. 16, a reflector670 that includes a FBG 520 may transmit out-of-band light (e.g.,optical noise, such as for example, ASE produced in gain fiber 660) sothat the light is dumped out of the reflector 670 and is not reflectedback into the gain fiber 660. In particular embodiments, a reflector 670that includes a FBG 520 may act as a spectral filter by removing greaterthan or equal to 50%, 60%, 80%, 90%, 95%, or 99% of the out-of-bandlight received by the reflector 670. As an example, greater than orequal to 90% of ASE light that is produced in the gain fiber 660 andthat propagates to reflector 670 may be transmitted through thereflector 670 and effectively removed from the amplifier 470. Inparticular embodiments, reflector 670 may include a FBG 520 thatreflects light at a pump-laser wavelength (e.g., 976 nm). Light frompump laser 640 that is not absorbed in the gain fiber 660 may bereflected by reflector 670 to make a second pass through the gain fiber660. This may result in an improvement in pumping efficiency since agreater fraction of pump-laser light may be absorbed by configuring thepump light to make two passes through the gain fiber 660.

In particular embodiments, reflector 670 may include two or more FBGs520 coupled together in series. As an example, reflector 670 may includea wavelength-dependent delay line similar to the wavelength-dependentdelay line 500 described above. In particular embodiments, a reflector670 with a wavelength-dependent delay line may include N FBGs 520 andN−1 fiber delays 530 connected together in series as illustrated in FIG.12. As an example, reflector 670 may include a wavelength-dependentdelay line that separates a broadband pulse of light into N time-delayedpulses of light or that separates N time-coincident pulses of light intoN time-delayed pulses of light. As another example, the input light tothe amplifier 470 may include N time-coincident pulses of light having Ndifferent wavelengths, and the output light from the amplifier 470 mayinclude N amplified pulses that are time delayed with respect to oneanother according to wavelength.

In particular embodiments, coupler 600A may be a fiber-optic splitter ortap coupler that splits off a portion of input light and sends it to PD610A. The remaining light that is not split-off propagates on toisolator 620A. Similarly, coupler 600B may be a tap coupler that splitsoff a portion of output light and sends it to PD 610B with the remaininglight proceeding to filter 630. The tap coupler 600A or 600B may coupleapproximately 0.5%, 1%, 2%, 3%, 5%, 10%, or any other suitablepercentage of light to PD 610A or PD 610B, respectively. As an example,input coupler 600A may split off approximately 10% of the input lightand direct it to PD 610A and send the remaining approximately 90% ofinput light on to the isolator 620A. As another example, output coupler600B may split off approximately 1% of the amplified light and direct itto PD 610B and send the remaining approximately 99% of the amplifiedlight on to the filter 630. In particular embodiments, an amplifier 470may include an input coupler 600A, an output coupler 600B, or both aninput coupler 600A and an output coupler 600B.

In particular embodiments, PD 610A or 610B may be a silicon, germanium,or InGaAs PN or PIN photodiode. In particular embodiments, coupler 600Aand PD 610A may be used to monitor the light coming into the amplifier470, and coupler 600B and PD 610B may be used to monitor the light afteramplification. As an example, PD 610A may receive the split-off inputlight from coupler 600A, and PD 610A may generate an electrical signalbased on the received light. Similarly, PD 610B may receive thesplit-off output light from coupler 600B, and PD 610B may generate anelectrical signal based on the output light. The electrical signal fromPD 610A or PD 610B may be sent to a processor or controller 150 formonitoring the status of the input or output light, respectively. If avoltage or current of the electrical signal from PD 610A drops below aparticular predetermined threshold level, then a processor or controller150 may determine that there is insufficient light coming into theamplifier 470. The amplifier 470 may be shut down or disabled (e.g., thepump laser 640 may be turned off or the amount of light it produces maybe reduced) to avoid possible damage to the amplifier 470. If a voltageor current of the electrical signal from PD 610B drops below aparticular predetermined threshold level, then a processor or controller150 may determine that there is a problem with amplifier 470 (e.g.,there may be a broken optical fiber, pump laser 640 may be failing, orone of the other components in amplifier 470 may be failing). Inparticular embodiments, signals from PD 610A or PD 610B may be used toadjust or monitor the gain or output power of amplifier 470. As anexample, a ratio of signals from PDs 610A and 610B may be used todetermine the gain of amplifier 470, and the amplifier gain may beadjusted by changing the pump-laser current (which changes the amount ofpump power provided by pump laser 640). As another example, a signalfrom PD 610B may be used to determine the output power of amplifier 470,and the amplifier output power may be adjusted by changing the currentsupplied to pump laser 640.

In particular embodiments, amplifier 470 may include an input opticalisolator 620A or an output optical isolator 620B. An optical isolator(620A, 620B) may include a Faraday rotator, and the operation of anoptical isolator may be based on the Faraday effect where thepolarization of light traveling through the isolator is rotated in thesame direction regardless of the direction of travel of the light. Inparticular embodiments, an optical isolator (620A, 620B) may be afiber-coupled device configured to reduce or attenuatebackward-propagating light. Backward-propagating light may originatefrom ASE light from a gain fiber 660 or from optical reflections at oneor more optical interfaces of the components in amplifier 470, and thebackward-propagating light may destabilize or cause damage to a seedlaser 400, laser diode 440 or amplifier 470. Isolators 620A and 620B inFIG. 16 are configured to allow light to pass in the direction of thearrow drawn in the isolator and block light propagating in the reversedirection. In FIG. 16, a laser diode 440 may provide the input light toamplifier 470, and isolator 620A may significantly reduce the amount ofbackward-propagating light that travels back to the laser diode 440. Theoutput of amplifier 470 in FIG. 16 may be coupled to a second amplifier,and isolator 620B may reduce the amount of light that propagates backinto the amplifier 470.

In FIG. 16, input isolator 620A may allow light to propagate fromcoupler 600A to port 1 of circulator 510, but any light propagating inthe reverse direction may be attenuated. As an example, back-reflectedlight propagating from port 1 of circulator 510 to isolator 620A may beattenuated by greater than or equal to 5 dB, 10 dB, 20 dB, 30 dB, 40 dB,50 dB, or any other suitable attenuation value. As another example, ifisolator 620A attenuates back-reflected light by greater than or equalto 30 dB, then less than or equal to 0.1% of light propagating from port1 of circulator 510 may be transmitted through the isolator 620A and tocoupler 600A. In particular embodiments, circulator 510 may perform anoptical isolation function. As an example, amplifier 470 may not includeisolator 620A or 620B, and circulator 510 may include one or moreoptical elements that act as an input or output optical isolator.

In particular embodiments, an amplifier 470 may include an opticalfilter 630. The output optical filter 630 in FIG. 16 may be configuredto remove greater than or equal to 50% of the optical noise propagatingtoward the amplifier output (e.g., the optical noise may include ASEproduced by the gain fiber 660). In particular embodiments, amplifier470 may include an optical filter 630 located at the amplifier input, anoptical filter 630 located at the amplifier output, or optical filters630 located at both the input and output of amplifier 470. In particularembodiments, amplifier 470 may include an optical filter 630 thatincludes a spectral filter (as described above with respect to FIG. 14)or a temporal filter (as described above with respect to FIG. 15). As anexample, amplifier 470 may include an optical filter 630 located at theinput to amplifier 470, and the optical filter 630 may include aspectral filter, a temporal filter, or a combination of spectral andtemporal filters. An input optical filter 630 may reduce the amount ofoptical noise (e.g., ASE from a previous amplifier stage) at the inputto an amplifier 470. In the example of FIG. 16, amplifier 470 includesan optical filter 630 located at the output of amplifier 470. An outputoptical filter 630 (which may include a spectral filter, a temporalfilter, or a combination of spectral and temporal filters) may reducethe amount of optical noise accompanying the amplified optical pulsesthat propagate out of amplifier 470. The optical noise may include ASEfrom gain fiber 660 that is coupled to port 3 of circulator and towardthe amplifier output. As an example, optical filter 630 in FIG. 16 mayremove greater than or equal to 80% of the ASE from the output ofamplifier 470.

FIG. 17 illustrates example absorption spectra for erbium and ytterbiumions incorporated into a glass host (e.g., fused silica). Erbiumexhibits an absorption spectrum that extends from approximately 950 nmto approximately 1020 nm. Ytterbium exhibits an absorption spectrum thatextends from approximately 890 nm to approximately 1020 nm. The erbiumand ytterbium ions have a peak absorption between approximately 970 nmand approximately 985 nm. As an example, an erbium-doped orytterbium-doped fiber amplifier 470 may be pumped with a pump laser 640having a wavelength of approximately 976 nm or 980 nm.

FIG. 18 illustrates example absorption and emission spectra for a glasshost doped with a combination of erbium and ytterbium. Theerbium/ytterbium emission spectra extends from approximately 1470 nm toapproximately 1630 nm. As an example an EYDFA with Er:Yb-doped gainfiber may be used to amplify light having wavelengths betweenapproximately 1470 nm and approximately 1630 nm.

FIG. 19 illustrates an example single-pass fiber-optic amplifier 470. InFIG. 19, input light makes a single pass through the gain fiber 660, andafter passing through the output of amplifier 470, the amplified outputlight may be sent to another amplifier 470, a demultiplexer, an opticallink 330, or a sensor head 310. In particular embodiments, a single-passamplifier 470 may include one or more optical filters (e.g., 630A or630B), couplers (e.g., 600A or 600B), photodiodes (e.g., 610A or 610B),isolators (e.g., 620A or 620B), gain fibers 660, pump lasers (e.g., 640Aor 640B), or pump WDMs (e.g., 650A or 650B). The single-pass amplifier470 illustrated in FIG. 19 has an input that includes an input filter630A, an input coupler 600A and PD 610A, and an input isolator 620A. Theoptical gain for the amplifier 470 is provided by pump lasers 640A and640B which are coupled to gain fiber 660 through pump WDMs 650A and650B, respectively. The gain fiber 660 in FIG. 19 may be an erbium-dopedor erbium/ytterbium-doped gain fiber 660. The single-pass amplifier 470illustrated in FIG. 19 has an output that includes an output isolator620B, an output coupler 600B and PD 610B, and an output filter 630B.

In particular embodiments, an amplifier 470 may include 1, 2, 3, or anyother suitable number of pump lasers 640. The double-pass amplifier 470in FIG. 16 includes one pump laser 640, and the single-pass amplifier470 in FIG. 19 includes two pump lasers (640A, 640B). In particularembodiments, a double-pass amplifier 470 may include one pump laser 640(as illustrated in FIG. 16), or a double-pass amplifier 470 may includetwo pump lasers 640 (e.g., one pump laser coupled to each end of thegain fiber 660). In particular embodiments, a single-pass amplifier 470may have one pump laser (e.g., pump laser 640A or 640B), or asingle-pass amplifier 470 may have two pump lasers (e.g., pump lasers640A and 640B). In particular embodiments, a pump laser may beco-propagating or counter-propagating with respect to the light that isamplified by an amplifier 470. In FIG. 19, pump laser 640A is aco-propagating pump laser (e.g., the pump-laser light propagates in thesame direction as the light that is amplified by the amplifier 470), andpump laser 640B is a counter-propagating pump laser (e.g., thepump-laser light propagates in the opposite direction to the light thatis amplified). In particular embodiments, one pump laser may be used toprovide pump light to both ends of a gain fiber 660. As an example, pumplaser 640A in FIG. 19 may be split (e.g., with a 3-dB fiber-optic powersplitter) into two fibers, where one fiber is coupled to pump WDM 650Aand the other fiber is coupled to pump WDM 650B. In particularembodiments, two or more pump lasers with different wavelengths may becombined together using a wavelength combiner or a WDM device. As anexample, light from a pump laser operating at 974 nm may be combinedwith light from a pump laser operating at 976 nm, and the combined974-nm/976-nm pump light may be coupled into a gain fiber 660. Inparticular embodiments, an amplifier 470 that includes multiple pumplasers may provide higher pump power to a gain fiber 660 or may provideredundant pump-laser sources in case one of the pump lasers fails.

FIG. 20 illustrates an example booster amplifier 470 that produces afree-space output beam 125. In particular embodiments, a boosteramplifier 470 may refer to an amplifier that sends an output beam 125 toa scanner 120 or a sensor head 310, or a booster amplifier 470 may referto an amplifier that provides a final amplification stage in a series oftwo or more amplifiers. As an example, booster amplifier 470 in FIG. 20may receive optical pulses that have been amplified by one or moreprevious amplifiers (e.g., a single-stage amplifier 470 or adouble-stage amplifier 470), and the booster amplifier 470 may produce afree-space output beam 125 that is directed to a scanner 120 or a sensorhead 310. As another example, booster amplifier 470 may receiveunamplified optical pulses (e.g., from a pulsed laser diode), andbooster amplifier 470 may provide a single stage of opticalamplification prior to sending a free-space output beam 125 to a scanner120. In particular embodiments, a booster amplifier 470 may include anoutput collimator 340 configured to receive amplified optical pulsesproduced in gain fiber 660 and produce a free-space optical beam 125that includes the amplified optical pulses. As an example, the boosteramplifier 470 in FIG. 20 may be a fiber-optic amplifier that isterminated at output collimator 340, and output collimator 340 mayproduce a free-space output beam 125.

In particular embodiments, a booster amplifier 470 may provide anysuitable amount of optical power gain, such as for example, a gain ofapproximately 3 dB, 5 dB, 7 dB, 10 dB, 15 dB, 20 dB, or 30 dB. As anexample, a booster amplifier 470 may receive pulses with a 100-mWaverage power and produce amplified pulses with a 1-W average power,corresponding to an optical gain of approximately 10 dB. In particularembodiments, a booster amplifier 470 may include a single pump laser 640(e.g., a co-propagating or counter-propagating pump laser) or two ormore pump lasers 640 (e.g., a co-propagating pump and acounter-propagating pump). As an example, a booster amplifier 470 mayinclude a counter-propagating pump laser 640 located on the output sideof the amplifier 470. In FIG. 20, the booster amplifier 470 includes aco-propagating pump laser 640 (along with a pump WDM 650) located on theinput side of the amplifier 470.

In particular embodiments, a booster amplifier 470 may include a gainfiber 660 that is a double-clad gain fiber 660. In particularembodiments, a double-clad gain fiber 660 may include a core, innercladding, and outer cladding, where the core is doped with a rare-earthmaterial. As an example, the core may be doped with erbium, or thedouble-clad gain fiber 660 may be a Er:Yb co-doped fiber where the coreis doped with a combination of erbium and ytterbium. The refractiveindices of the core, inner cladding, and outer cladding may beconfigured so that the pump-laser light is confined to propagateprimarily in the inner cladding, and the amplified light is confined topropagate primarily in the core. In particular embodiments, adouble-clad gain fiber 660 may have a core with any suitable diameter,such as for example, a diameter of approximately 7 μm, 8 μm, 9 μm, 10μm, 12 μm, 20 μm, or 25 μm. In particular embodiments, gain fiber 660may be a double-clad photonic-crystal fiber that includes a core dopedwith rare-earth material where the core is surrounded by an arrangementof holes that extend along the length of the gain fiber 660.

In particular embodiments, amplifier 470 may include a cladding powerstripper 680, which may also be referred to as a cladding mode stripper.A cladding power stripper 680 may be used to absorb or remove light fromthe inner cladding or outer cladding in a double-clad gain fiber 660. Asan example, cladding power stripper 680 may be located on the oppositeside of the gain fiber 660 from the pump laser 640, and the claddingpower stripper 680 may remove residual, unabsorbed pump-laser light thatpropagates through the gain fiber 660 without being absorbed in the gainfiber 660. As an example, the residual pump-laser light may be removedfrom the inner cladding of the gain fiber 660 to prevent the residualpump light from accompanying the amplified pulses as they exit theamplifier 470. Additionally, the cladding power stripper 680 may removeASE produced by the gain fiber 660 that propagates in the inner or outercladding.

FIG. 21 illustrates an example lidar system 100 that includes threeamplifiers 470 (amplifier 1, amplifier 2, and amplifier 3). In theexample of FIG. 21, lidar system 100 includes laser 300, fiber-opticlink 330, and sensor 310. Laser 300 includes seed laser 400, amplifier1, and the input portion of amplifier 2, and fiber-optic link 330includes the gain fiber 660 of amplifier 2. The sensor head 310 includesamplifier 3 and scanner 120 along with the output portion (e.g., filter630B) of amplifier 2. In particular embodiments, amplifier 1 may be adouble-pass amplifier (e.g., similar to the double-pass amplifier 470illustrated in FIG. 16), and amplifier 2 may be a single-pass amplifier(e.g., similar to the single-pass amplifier 470 illustrated in FIG. 19).Amplifier 1 may act as a preamplifier and amplify seed pulses from seedlaser 400. Amplifier 2 may act as a mid-stage amplifier that receivesand amplifies the pulses from amplifier 1. Amplifier 3 may act as abooster amplifier (e.g., similar to the booster amplifier 470illustrated in FIG. 20) that provides a final amplification stage andproduces a free-space output beam 125 that is sent to scanner 120. Inparticular embodiments, light may be coupled into or out of an amplifier470 by an optical fiber (e.g., a SM fiber, MM fiber, PM fiber, LMAfiber, photonic-crystal fiber, or photonic-bandgap fiber), or light maybe coupled into or out of an amplifier by a free-space beam (e.g., anamplifier output may be terminated by a free-space collimator 340).

In particular embodiments, a lidar system 100 may include a laser 300with one or more optical amplifiers 470, and the lidar system 100 mayinclude multiple optical links 330. Each optical link 330 may include again fiber 660 of an optical amplifier 470, where the gain fiber 660 isdistributed along part of or substantially all of the optical link 330.In FIG. 21, laser 300 includes amplifier 1, and optical link 330includes the gain fiber 660 of amplifier 2. In FIG. 21, gain fiber 660is part of the fiber-optic link 330, and gain fiber 660 amplifiesoptical pulses while the pulses are conveyed from laser 300 to sensor310. In particular embodiments, each optical link 330 of a lidar system100 may include a gain fiber 660 of a fiber-optic amplifier 470, wherethe gain fiber 660 is configured to amplify pulses of light receivedfrom a seed laser 400, a laser diode 440, or a previous amplifier 470.In FIG. 21, the gain fiber 660 amplifies pulses of light while the lightpropagates from laser 300 to a corresponding sensor head 310.Additionally, the gain fiber 660 forms at least part of the optical link330 between laser 300 and a corresponding sensor head 310.

In particular embodiments, one or more components of an amplifier 470may be located in one or more different parts of lidar system 100, andthe amplifier 470 may be referred to as a distributed amplifier 470. Asan example, a distributed amplifier 470 may include one or more filters630, isolators 620, couplers 600, PDs 610, pump lasers 640, pump WDMs650, or gain fibers 660 located at least in part in laser 300,fiber-optic link 330, or sensor head 310. As another example, adistributed amplifier 470 may include one pump laser 640 located inlaser 300 or sensor 310 (e.g., the pump laser 640 may be co-propagatingor counter-propagating). As another example, a distributed amplifier 470may include one pump laser 640 located in laser 300 and another pumplaser 640 located in sensor 310. In the example of FIG. 21, amplifier 2is a distributed amplifier 470 where input filter 630A, input isolator620, pump laser 640, and pump WDM 650 are located in laser 300, andoutput filter 630B is located in sensor 310.

In particular embodiments, a lidar system 100 may include multiplesensor heads 310, where each sensor head includes one or more opticalamplifiers 470 (e.g., a preamplifier, a mid-stage amplifier, or abooster amplifier), which may be referred to as sensor-head amplifiers470. A sensor-head amplifier 470 may be configured to receive pulses oflight from a corresponding optical link 330 and amplify the receivedpulses of light. The sensor-head amplifier 470 may amplify pulses oflight conveyed to the sensor head 310 by an optical link 330, and afteramplifying the pulses, the sensor-head amplifier 470 may direct theamplified pulses of light to a scanner 120 for scanning across a fieldof regard of the sensor head 310. In FIG. 21, sensor head 310 includesfilter 630B, amplifier 3, and scanner 120. Amplifier 3 is a sensor-headamplifier 470 that receives pulses from fiber-optic link 330 via filter630B, amplifies the received pulses, and sends the amplified pulses toscanner 120. In particular embodiments, a sensor-head amplifier 470 maybe a fiber-optic amplifier or a free-space amplifier.

In particular embodiments, a lidar system 100 may include a laser system(which may be referred to as a light source) that is contained within apart of the lidar system 100 (e.g., within laser 300), or a lidar system100 may include a distributed laser system that is contained within twoor more parts of the lidar system 100. As an example, a laser systemthat produces and amplifies optical pulses may be located within laser300 or within sensor head 310. As another example, one or more parts ofa distributed laser system that produces and amplifies optical pulsesmay be located or contained within laser 300, fiber-optic link 330, orsensor head 310. FIG. 21 illustrates a distributed laser system thatincludes seed laser 400, amplifier 1, amplifier 2, and amplifier 3,where parts of the laser system are located in laser 300, fiber-opticlink 330, and sensor head 310.

In particular embodiments, a lidar system 100 may include a laser systemthat includes: a seed laser 400; a first fiber-optic amplifier 470; afirst optical filter 630A; and a second fiber-optic amplifier 470. Inparticular embodiments, the laser system may also include a secondoptical filter 630B, or the laser system may also include a thirdfiber-optic amplifier 470. The seed laser 400 may produce optical seedpulses which are amplified by the first amplifier 470 with a firstamplifier gain (e.g., 10 dB, 20 dB, 30 dB or 40 dB) to produce afirst-amplifier output that includes amplified seed pulses and ASE. Thefirst optical filter 630A (which may include a spectral filter, atemporal filter, or a combination of a spectral filter and temporalfilter) may remove from the first-amplifier output an amount of the ASE(e.g., remove approximately 50%, 60%, 70%, 80%, 90%, 95%, or 99% of theASE). The second amplifier 470 may receive the amplified seed pulsesfrom the first optical filter and amplify the received pulses by asecond amplifier gain (e.g., 10 dB, 20 dB, 30 dB or 40 dB) to produceoutput pulses. In particular embodiments, the output pulses may be sentto a third amplification stage, to a demultiplexer 410, to a fiber-opticlink 330, or to a scanner 120 of a sensor 310. In particularembodiments, the laser system may include a second optical filter 630B(which may include a spectral filter, a temporal filter, or acombination of a spectral filter and a temporal filter) that receivesthe output pulses from the second amplifier 470 and removes an amount ofASE produced by the second amplifier 470 (e.g., removes approximately50%, 60%, 70%, 80%, 90%, 95%, or 99% of the ASE). In particularembodiments, the laser system may include a third amplifier 470 thatreceives the output pulses from the second amplifier 470 and amplifiesthe pulses by a third amplifier gain (e.g., 10 dB, 20 dB, 30 dB or 40dB). In particular embodiments, the amplified pulses from the thirdamplifier 470 may be sent to a fourth amplification stage, to ademultiplexer 410, to a fiber-optic link 330, or to a scanner 120 of asensor 310.

In particular embodiments, the optical seed pulses produced by a seedlaser 400 may have an average power of greater than or equal to 1 μW,and the output pulses from a second amplifier 470 may have an averagepower of greater than or equal to 1 mW. In particular embodiments, thefirst amplifier gain and the second amplifier gain together maycorrespond to an overall optical power gain of greater than or equal to40 dB (e.g., the sum of the first amplifier gain and the secondamplifier gain may be greater than or equal to 40 dB). As an example,the first amplifier gain may be approximately equal to 10 dB, 20 dB, or30 dB, and the second amplifier gain may be approximately equal to 10dB, 20 dB, or 30 dB. As another example, the first amplifier gain may beapproximately equal to 30 dB, and the second amplifier gain may beapproximately equal to 20 dB, corresponding to an overall gain ofapproximately 50 dB.

In particular embodiments, the first fiber-optic amplifier 470 of alaser system may include a single-pass amplifier (e.g., with anerbium-doped or erbium/ytterbium-doped gain fiber 660), and the secondfiber-optic amplifier 470 may include another single-pass amplifier(e.g., with an erbium-doped or erbium/ytterbium-doped gain fiber 660).In particular embodiments, the first fiber-optic amplifier 470 of alaser system may include a double-pass amplifier (e.g., with acirculator 510, a gain fiber 660, and one or more FBGs 520), and thesecond fiber-optic amplifier 470 may include a single-pass amplifier(e.g., with an erbium-doped or erbium/ytterbium-doped gain fiber 660).Additionally, the laser system may also include a third fiber-opticamplifier 470, where the third amplifier 470 is a booster amplifier(e.g., with a double-clad gain fiber 660 that includes erbium dopants orerbium and ytterbium dopants). In particular embodiments, the firstfiber-optic amplifier 470 may include a single-pass or double-passamplifier, and the second fiber-optic amplifier 470 may include abooster amplifier that sends a free-space output beam 125 to a scanner120 of a sensor 310 (e.g., the first amplifier 470 may be located inlaser 300 and the second amplifier 470 may be located in sensor 310).The lidar system 100 in FIG. 21 may be referred to as having a lasersystem that includes seed laser 400, amplifier 1, amplifier 2, andamplifier 3. Amplifiers 1, 2, and 3 may correspond to the first, second,and third amplifiers, respectively, as described above. Additionally,filters 630A and 630B in FIG. 21 may correspond to the first and secondoptical filters as described above.

In particular embodiments, the output pulses produced by a laser systemwith two or three stages of amplification may have output-pulsecharacteristics that include one or more of the following: a pulserepetition frequency of less than or equal to 100 MHz (e.g.,approximately 500 kHz, 640 kHz, 750 kHz, 1 MHz, 2 MHz, 4 MHz, 5 MHz, 10MHz, 20 MHz, 50 MHz, or 100 MHz); a pulse duration of less than or equalto 20 nanoseconds (e.g., approximately 200 ps, 400 ps, 500 ps, 800 ps, 1ns, 2 ns, 4 ns, 8 ns, 10 ns, 15 ns, or 20 ns); a duty cycle of less thanor equal to 1% (e.g., approximately 0.01%, 0.02%, 0.05%, 0.1%, 0.2%,0.5%, or 1%); an operating wavelength of between 1400 nm and 2050 nm; apulse energy of greater than or equal to 10 nanojoules (e.g.,approximately 10 nJ, 50 nJ, 100 nJ, 500 nJ, 1 μJ, 2 μJ, 5 μJ, or 10 μJ);a peak pulse power of greater than or equal to 1 watt (e.g.,approximately 1 W, 10 W, 50 W, 100 W, 200 W, 500 W, 1 kW, 2 kW, or 10kW); or an average power of less than or equal to 50 watts (e.g.,approximately 50 W, 20 W, 10 W, 5 W, 2 W, 1 W, 0.5 W, or 0.1 W). As anexample, a laser system may produce an output beam 125 with a pulserepetition frequency of between approximately 500 kHz and approximately750 kHz, and the pulses may have a pulse duration between approximately500 ps and approximately 5 ns. As another example, a laser system mayproduce pulses with a pulse repetition frequency of approximately 750kHz and a pulse duration of approximately 1 ns, corresponding to a dutycycle of approximately 0.075%. As another example, a laser system mayproduce pulses with a pulse repetition frequency of approximately 1 MHzand a pulse duration of approximately 5 ns, corresponding to a dutycycle of approximately 0.5%. As another example, a laser system mayproduce pulses with a pulse duration of approximately 10 ns and a pulseenergy of approximately 100 nJ, which corresponds to pulses with a peakpower of approximately 10 W. As another example, a laser system mayproduce pulses with a pulse duration of approximately 700 ps and a pulseenergy of approximately 1 μJ, which corresponds to pulses with a peakpower of approximately 1.4 kW. As another example, a laser system mayproduce pulses with a pulse energy of approximately 2 μJ and a pulserepetition frequency of approximately 1 MHz, corresponding to an averagepower of approximately 2 W. As another example, a laser system mayproduce an output beam 125 with an average power of less than or equalto 50 W, where the output beam 125 includes ASE that makes up less thanor equal to 1%, 5%, 10%, or 25% of the average power, and the opticalpulses in the output beam 125 make up greater than or equal to 99%, 95%,90%, or 75% of the average power, respectively.

In particular embodiments, an optical amplifier 470 may include anysuitable number or type of optical components having any suitablearrangement. In particular embodiments, an amplifier 470 may includesome, none, or all of the components illustrated in FIG. 16, 19, 20, or21. In particular embodiments, an amplifier 470 may include 0, 1, 2, orany other suitable number of couplers and associated PDs. As an example,an amplifier 470 may include only one coupler with an associated PD(e.g., an input coupler 600A and PD 610A or an output coupler 600B andPD 610B), or an amplifier 470 may include both an input coupler 600A andan output coupler 600B (along with associated PDs 610A and 610B), asillustrated in FIG. 16. As another example, an amplifier 470 may includea coupler and PD configured to tap off and monitor light from a pumplaser 640. As another example, an amplifier 470 may include neither aninput coupler 600A nor an output coupler 600B. In particularembodiments, an amplifier 470 may include 0, 1, 2, or any other suitablenumber of optical isolators. As an example, an amplifier 470 may includean input isolator 620A or an output isolator 620B, or an amplifier 470may include both an input isolator 620A and an output isolator 620B, asillustrated in FIG. 16. An amplifier 470 may not have an input isolator620A if it receives input optical pulses produced by a laser diode 440that includes an optical isolator in its package. In particularembodiments, an amplifier 470 may include 0, 1, 2, or any other suitablenumber of optical filters 630. As an example, an amplifier 470 mayinclude only one optical filter 630 (e.g., a filter located at an inputor output of amplifier 470), or an amplifier 470 may include opticalfilters 630 located at both the input and output of amplifier 470.

In particular embodiments, an amplifier 470 may include any suitableoptical components arranged in any suitable order. As an example, anamplifier 470 may include a filter 630 followed by an isolator (620A,620B), or vice versa. In particular embodiments, an amplifier input mayinclude a filter 630, coupler 600A, isolator 620A, or any other suitablecomponent arranged in any suitable order. As an example, an amplifierinput may include a coupler 600A followed by an isolator 620A, or anamplifier input may include an isolator 620A followed by a coupler 600A.Additionally, an amplifier input may include a filter 630 located beforeor after a coupler 600A or isolator 620A. The amplifier 470 in FIG. 16has an input that includes coupler 600A followed by isolator 620A. Inparticular embodiments, an amplifier output may include an isolator620B, coupler 600B, PD 610 B, filter 630, or any other suitablecomponent arranged in any suitable order. For example, an amplifieroutput may include an isolator 620B followed by a filter 630, or viceversa. In FIG. 16, the amplifier output includes isolator 620B followedby coupler 600B, which is followed by filter 630.

In particular embodiments, two or more optical components may becombined together into a single fiber-optic package. As an example,rather than having a discrete or separate coupler 600A and isolator620A, the two components may be combined together into a single packagethat includes a coupler 600A and an isolator 620A. The package may havethree fiber-optic ports: one input port, one output port, and one portfor split-off light to be sent to a PD 610A. As another example, acoupler 600A, isolator 620A, and PD 610A may be combined together into asingle package. As another example, isolator 620A and pump WDM 650A maybe packaged together in a single package. As another example, pump WDM650B and tap coupler 600B may be combined together into a singlepackage. As another example, isolator 620A, pump WDM 650A, and tapcoupler 600A may be combined together into a single package. As anotherexample, isolator 620 and collimator 340 may be combined together into asingle package.

In particular embodiments, all or most of the optical components of anamplifier 470 may be packaged together within a single housing, where ahousing may refer to a box, case, or enclosure that holds or containsthe amplifier components. As an example, the components illustrated inFIG. 16 or FIG. 19 may be packaged together in a single housing, and thehousing may have an input fiber and an output fiber. The housing mayalso include one or more electrical connections for conveying electricalpower or electrical signals to or from the amplifier 470. As anotherexample, the components illustrated in FIG. 20 may be packaged togetherin a single housing, and the housing may have an input fiber and mayproduce a free-space output beam 125. In particular embodiments, theoptical components for two or more amplifiers 470 may be packagedtogether within a single housing. As an example, a housing may containthe optical components for a double-pass amplifier (e.g., amplifier 470of FIG. 16) and the optical components for a single-pass amplifier(e.g., amplifier 470 of FIG. 19). The two amplifiers may be coupledtogether forming a two-stage optical amplifier. In particularembodiments, the optical components for a laser 300 may be packagedtogether within a single housing. As an example, the seed laser 400 andamplifier 1 illustrated in FIG. 21 may be packaged together into asingle housing. As another example, the seed laser 400, amplifier 1, andinput portion of amplifier 2 illustrated in FIG. 21 may be packagedtogether into a single housing. In particular embodiments, a seed laser400 and one or more amplifier stages 470 may be packaged together into asingle housing. As an example, a seed laser 400, a first-stage amplifier(e.g., amplifier 470 of FIG. 16), and a second-stage amplifier (e.g.,amplifier 470 of FIG. 19) may be packaged together within a singlehousing. Additionally, the two amplifiers 470 may include an opticalfilter 630 that is disposed between the amplifiers.

In particular embodiments, a conventional laser system with one or morefiber-optic amplifiers may exhibit optical nonlinearities associatedwith the propagation of relatively short-duration or relatively highpeak-power optical pulses in optical fiber. As an example, opticalnonlinearities such as self-phase modulation (SPM), Raman effects (e.g.,Raman scattering), or four-wave mixing (FWM) may cause a reduction ingain of an amplifier 470, temporal or spectral distortion of opticalpulses, or the generation of unwanted light (e.g., light at differentwavelengths from the optical pulses). In particular embodiments, a lidarsystem 100 as described or illustrated herein may provide a reduction ormitigation of effects associated with optical nonlinearities. As anexample, a laser system with a fiber-optic link 330 that includes a gainfiber 660 to amplify pulses on the way to a sensor head 310 may reducethe need for additional optical fiber that may contribute to unwantednonlinear-optical effects in the fiber. As another example, use ofoptical fiber with larger core diameters (e.g., LMA fiber) may reducethe optical intensity in the optical fiber, which may lead to areduction in nonlinear-optical effects. As another example, a lidarsystem 100 with a sensor head 310 that includes a booster amplifier 470may exhibit reduced nonlinear-optical effects since the finalamplification stage is located in the sensor head 310 and the opticalpulses may not need to propagate through additional optical fiber afterbeing amplified by the booster amplifier 470.

In particular embodiments, a laser system as described or illustratedherein may allow the production of optical pulses having a substantiallylower duty cycle, lower pulse repetition frequency, longer pulse period,or higher pulse energy than a conventional laser system. As an example,a laser system as described or illustrated herein may include one ormore optical isolators 620 or optical filters 630, which may impede orprevent an optical amplifier 470 of the laser system from emittingunwanted spurious light (e.g., spurious light may be produced throughQ-switching or self-lasing). An optical isolator 620 may prevent theemission of spurious light by blocking ASE or reflected light frompropagating backwards through an amplifier 470, and an optical filter630 may prevent the emission of spurious light by removing unwantedoptical noise from a laser system. The emission of spurious light may beinhibited during the time between successive optical pulses propagatingthrough and being amplified by an amplifier 470. By preventing theproduction of spurious light between pulses, a laser system as describedor illustrated herein may be able to operate with a lower duty cycle orlower pulse repetition frequency than a conventional laser system.

FIG. 22 illustrates an example lidar system 100 with a laser 300 thatincludes a seed laser 400 and an amplifier 470. In particularembodiments, laser 300 may include a seed laser 400 and one or moreamplifiers 470 that amplify optical pulses produced by the seed laser400. As an example, laser 300 may include a seed laser 400 that producesoptical pulses which are amplified by one amplifier 470 located in laser300. The amplified pulses may also be amplified by one or moreadditional amplifiers 470 located in laser 300, optical link 330, orsensor head 310. As an example, amplifier 470 in laser 300 may be asingle-pass amplifier or a double-pass amplifier, and the lidar system100 may include one or more additional single-pass or double-passamplifiers or a booster amplifier with a double-clad gain fiber 660.

FIG. 23 illustrates an example lidar system 100 with an optical link 330that includes an amplifier 470. In particular embodiments, an amplifier470 may be referred to as being located or included in an optical link330 if a gain fiber 660 of the amplifier is located in the optical link330. As an example, optical link 330 may include the gain fiber 660 ofan amplifier 470, and laser 300 or sensor 310 may include one or moreother components of the amplifier 470 (e.g., coupler 600A or 600B, PD610A or 610B, isolator 620, filter 630, pump laser 640, or pump WDM650). In particular embodiments, seed laser 400 may be located in laser300 and may produce optical pulses which are amplified by an amplifier470 located in optical link 330. As an example, the seed-laser pulsesmay be split by a demultiplexer 410 and coupled to multiple opticallinks 330 of a lidar system 100, and each optical link 330 may includean amplifier 470. The seed-laser pulses may also be amplified by one ormore additional amplifiers located in laser 300 or sensor 310. As anexample, laser 300 may include an amplifier 470, and the amplifier 470in optical link 330 may act as a booster amplifier. As another example,the amplifier in optical link 330 may act as a preamplifier or amid-stage amplifier, and the sensor head 310 may include a boosteramplifier 470 that produces a free-space output beam 125.

FIG. 24 illustrates an example lidar system 100 with a sensor head 310that includes an amplifier 470. In particular embodiments, a sensor head310 of a lidar system 100 may include an optical amplifier 470 thatreceives optical pulses from a corresponding optical link 330 andamplifies the received pulses. In particular embodiments, seed laser 400may be located in laser 300 and may produce optical pulses which areamplified by an amplifier 470 located in sensor head 310. Thesensor-head amplifier 470 in FIG. 24 may act as a booster amplifier thatproduces a free-space output beam 125. Additionally, prior to reachingthe sensor-head booster amplifier 470, the seed-laser pulses may beamplified by one or more additional preamplifiers or mid-stageamplifiers located in laser 300, optical link 330, or sensor head 310.

In particular embodiments, a gain fiber 660 of an amplifier 470 may belocated in a sensor head 310, and the pump laser 640 of the amplifier470 may be located in laser 300. As an example, light from a pump laser640 located in laser 300 may be sent to the sensor head 310 via anoptical fiber that is separate from the optical link 330. As anotherexample, light from a pump laser 640 may be combined with optical pulsesproduced in laser 300, and the combined pump light and pulses may besent to a sensor head 310 via the same optical link 330. For example,the optical link 330 may include a double-clad fiber configured toconvey both the pump light and the optical pulses produced in laser 300to the sensor head 310. The double-clad fiber, which may include a core,inner cladding, and outer cladding, may not include rare-earth dopantsand may not perform optical amplification. The optical pulses producedin laser 300 may propagate substantially in the core of the double-cladfiber, and the pump light may propagate substantially in the innercladding. The gain fiber in the sensor head 310 may be a double-cladgain fiber 660 that is pumped by the pump light and amplifies theoptical pulses from the laser 300.

In particular embodiments, a lidar system 100 may include a laser systemwith a combination of two or more of the configurations illustrated inFIGS. 22-24. As an example, a laser system may include two opticalamplifiers 470 having any suitable configuration, such as for example: afirst amplifier 470 located in laser 300 and a second amplifier 470located in optical link 330 or sensor head 310; a first amplifier 470located in optical link 330 and a second amplifier located 470 in sensorhead 310; two amplifiers 470 located in laser 300; or two amplifiers 470located in sensor head 310. As another example, a laser system mayinclude three optical amplifiers 470 having any suitable configuration,such as for example: a first amplifier 470 located in laser 300, asecond amplifier 470 located in optical link 330, and a third amplifier470 located in sensor head 310; two amplifiers 470 located in laser 300and a third amplifier 470 located in optical link 330 or sensor head310; one amplifier 470 located in laser 300 and two amplifiers 470located in sensor head 310; three amplifiers 470 located in laser 300;or three amplifiers 470 located in sensor head 310. In particularembodiments, the amplifiers 470 may have one or more optical filters 630disposed between two amplifiers 470 or located at an amplifier input oroutput.

In particular embodiments, a laser system may be part of a lidar system100 that includes a laser 300, an optical link 330, and a sensor head310. The laser system may include a seed laser 400, a first fiber-opticamplifier 470, and a second fiber-optic amplifier 470. The seed laser400 may produce optical pulses which are amplified by the first andsecond amplifiers 470. The seed laser 400 may be located in the laser300, and the optical link 330 may couple the laser 300 to the sensorhead 310. The first amplifier 470 may be located in the laser 300, theoptical link 330, or the sensor head 310. The second amplifier 470 maybe located in the laser 300, the optical link 330, or the sensor head310. As an example, the first amplifier 470 and the second amplifier 470may both be located in the laser 300. As another example, the firstamplifier 470 may be located in the laser 300, and the second amplifier470 may include a gain fiber 660 distributed along a length of theoptical link 330. As another example, the first amplifier 470 may belocated in laser 300, and the second amplifier 470 may be a boosteramplifier located in the sensor head 310. As another example, the firstamplifier 470 may be located in the optical link 330, and the secondamplifier 470 may be located in the sensor head 310 (e.g., the secondamplifier 470 may be a booster amplifier that produces a free-spaceoutput beam 125). As another example, the first and second amplifiers470 may be located in the laser 300, and the laser system may alsoinclude a third fiber-optic amplifier 470 that is also located in thelaser 300. As another example, the first and second amplifiers 470 maybe located in the laser 300, and the laser system may also include athird fiber-optic amplifier 470 that includes a gain fiber 660distributed along a length of the optical link 330. As another example,the first and second amplifiers 470 may be located in the laser 300, andthe laser system may also include a third amplifier 470 located in thesensor head (e.g., the third amplifier 470 may be a fiber-opticamplifier or a free-space amplifier). As another example, the firstamplifier 470 may be located in the laser 300, the second amplifier 470may include a gain fiber 660 distributed along a length of the opticallink 330, and the laser system may also include a third amplifier 470located in the sensor head.

FIG. 25 illustrates an example lidar system 100 where the sensor head310 includes an amplifier 470 coupled to an output collimator 340. Inparticular embodiments, a lidar system 100 may include a sensor head 310with a fiber-optic amplifier 470. The fiber-optic amplifier 470 may be abooster amplifier with a double-clad gain fiber 660 that amplifiespulses from a previous optical amplifier 470. The previous opticalamplifier 470 may be located in the sensor head 310, in optical link330, or in laser 300. In the example of FIG. 25, the sensor-headamplifier 470 may be a booster amplifier with a fiber-optic output thatis terminated at output collimator 340. The output collimator 340 mayproduce a free-space output beam 125 that is directed through mirror 115and to scanner 120.

FIG. 26 illustrates an example lidar system 100 where the sensor head310 includes a free-space amplifier 470. In particular embodiments, afree-space amplifier 470 may refer to an optical amplifier thatamplifies a free-space optical beam (e.g., the beam that is amplified isnot propagating through an optical fiber). In FIG. 26, the free-spaceamplifier 470 receives optical pulses in a free-space optical beam fromcollimator 340, and the free-space amplifier 470 amplifies the opticalpulses and sends the amplified output pulses to mirror 115 and scanner120. The free-space amplifier 470 may act as a booster amplifier thatamplifies a free-space input beam and produces an amplified free-spaceoutput beam 125. In particular embodiments, a free-space amplifier 470may include a pump laser 700 and a gain crystal 710. As an example, thepump laser 700 may produce a free-space pump beam that is directed orcoupled into the gain crystal 710. The pump laser 700 may have anysuitable operating wavelength, such as for example, approximately 908nm, 915 nm, 940 nm, 960 nm, 976 nm, 980 nm, 1050 nm, 1064 nm, 1450 nm,or 1480 nm. The gain crystal 710 may include any suitable materialconfigured to absorb light from the pump laser 700 and provide gain to afree-space optical beam that passes through the gain crystal 710. As anexample, the gain crystal 710 may include neodymium-doped yttriumaluminum garnet (Nd:YAG), neodymium-doped yttrium aluminum borate(Nd:YAB), erbium-doped glass, or glass or YAB doped with erbium (e.g.,Er:YAB) or doped with erbium and ytterbium (e.g., Er:Yb:YAB).

FIG. 27 illustrates an example laser 300 where the seed laser 400 iscombined with a supplemental light source 720. In particularembodiments, a laser system may include one or more seed lasers 400 thatproduce optical pulses and one or optical amplifiers 470 that amplifythe seed-laser pulses. The laser system may also include a supplementallight source 720 that is combined with the one or more seed lasers 400before proceeding to an amplifier 470. In particular embodiments, thesupplemental light source 720 may include a laser diode or alight-emitting diode (LED). Light from the supplemental light source 720may be combined with light from the seed laser 400 by a combiner 730,which may include a wavelength combiner or an optical switch. As anexample, the wavelength of the supplemental light source 720 may bedifferent from the seed-laser wavelength, and the combiner 730 mayinclude a wavelength combiner that combines the two wavelengths togetheronto a single fiber-optic output which is coupled to amplifier 470. Forexample, the seed-laser wavelength may be approximately 1550 nm, and thesupplemental-light-source wavelength may be approximately 1530 nm. Asanother example, combiner 730 may include a 2×1 optical switchconfigured so that light from either the seed laser 400 or thesupplemental light source 720 is sent to the amplifier 470. The opticalswitch may be synchronized to the seed laser 400 so that when the seedlaser 400 emits a pulse, the optical switch directs the pulse to theamplifier 470, and between seed-laser pulses, the optical switch maydirect light from the supplemental light source 720 to the amplifier470.

In particular embodiments, light from the supplemental light source 720may impede or prevent an optical amplifier 470 from spontaneouslyemitting spurious light (e.g., emitting an optical pulse throughQ-switching or self-lasing). The supplemental light source 720 maysuppress or prevent the optical amplifier 470 from emitting spuriousoptical pulses during times between when a seed-laser pulse is present(e.g., during a time after a first seed-laser pulse is amplified andprior to the receipt of a subsequent second seed-laser pulse).Additionally, light from the supplemental light source 720 may reducethe amount of ASE emitted by the amplifier 470. Light from thesupplemental light source 720 may be amplified by the amplifier 470,which may prevent the gain in the amplifier 470 from building up to alevel where spurious light may be produced or where excessive ASE isemitted.

In particular embodiments, a laser system may include a filter 630 thatremoves ASE light produced by the amplifier 470 or removes light fromthe supplemental light source 720 that was amplified by the amplifier470. As an example, the filter 630 may be a spectral filter that removesor attenuates light at the wavelength of the supplemental light source720. Additionally, the filter 630 may also remove or attenuate ASElight. As another example, the filter 630 may be an optical switch thatis synchronized to the seed laser 400 or the supplemental light source720. When an amplified seed-laser pulse is present, the optical switchmay switch to an open or transmitting state that allows the pulse topropagate to the output. During times between seed-laser pulses, theoptical switch may switch to a non-transmitting state to block lightfrom the supplemental light source 720 as well as ASE light from theamplifier 470. In particular embodiments, the supplemental light source720 may be configured to emit light in a CW mode or in a pulsed mode. Asan example, the supplemental light source 720 may be operated in apulsed mode in which the supplemental light source 720 is turned on inbetween seed-laser pulses and turned off when a seed-laser pulse ispresent. Additionally, the filter 630 may be an optical switchconfigured to block the transmission of light during times when thesupplemental light source 720 is turned on, and when an amplifiedseed-laser pulse is present, the optical switch may change to atransmitting state to allow the pulse to propagate to the output.

FIG. 28 illustrates an example laser 300 that includes a seed laser 400,amplifier 470, and demultiplexer 410. In particular embodiments, laser300 may include a seed laser 400, one or more optical amplifiers 470,and one or more demultiplexers 410. As an example, optical pulses fromseed laser 400 may be amplified by two or more amplifiers 470 coupled inseries before proceeding to demultiplexer 410. In the example of FIG.28, light from the seed laser 400 is amplified by amplifier 470 prior tobeing sent to demultiplexer 410 for distribution to the N optical links(330-1, 330-2, . . . , 330-N). In particular embodiments, laser 300 mayinclude a 1×N optical demultiplexer configured to receive amplifiedseed-laser pulses from amplifier 470 and distribute the amplifiedseed-laser pulses between N optical links (330-1, 330-2, . . . , 330-N)coupled to N respective sensor heads 310. In particular embodiments,laser 300 may include one or more optical amplifiers located after thedemultiplexer 410. As an example, laser 300 may include N opticalamplifiers (not illustrated in FIG. 28) located after the demultiplexer410, where each amplifier is configured to amplify light prior tosending the light to a corresponding optical link 330.

FIG. 29 illustrates an example laser 300 that includes multiple laserdiodes (440-1, 440-2, . . . , 440-N), a multiplexer 412, an amplifier470, and a demultiplexer 410. In particular embodiments, laser 300 mayinclude one or more laser diodes 440, one or more multiplexers 412, oneor more optical amplifiers 470, and one or more demultiplexers 410. Inthe example of FIG. 29, optical pulses from N laser diodes (440-1,440-2, . . . , 440-N) are combined together into a single optical fiberby multiplexer 412, and the combined optical pulses are amplified byamplifier 470. After amplification, demultiplexer 410 receives theamplified laser-diode pulses from amplifier 470 and distributes theamplified pulses between the N optical links (330-1, 330-2, . . . ,330-N). In particular embodiments, there may be two or more opticalamplifiers 470 located between multiplexer 412 and demultiplexer 410. Inparticular embodiments, the N laser diodes (440-1, 440-2, . . . , 440-N)may produce optical pulses at N different wavelengths, and multiplexer412 may be a wavelength combiner that combines the N wavelengths of theN respective laser diodes together into a single optical fiber coupledto amplifier 470. After the pulses are amplified by the opticalamplifier 470, the demultiplexer 410 may separate the pulses bywavelength and send them to a corresponding optical link. As an example,pulses from laser diode 440-1 may be directed by the demultiplexer 410to optical link 330-1, pulses from laser diode 440-2 may be directed tooptical link 330-2, and pulses from laser diode 440-N may be directed tooptical link 330-N. As another example, laser 300 may include 6 laserdiodes operating at 6 different wavelengths between approximately 1530nm and approximately 1560 nm. Each laser diode may be a pulsed laserdiode that produces pulses with a pulse repetition frequency ofapproximately 700 kHz. The laser-diode pulses may be synchronized andtime delayed with respect to one another, and when the pulses areinterleaved together by multiplexer 412, the combined pulses may have apulse repetition frequency of approximately 4.2 MHz. After amplificationby amplifier 470, the 4.2-MHz stream of amplified pulses may beseparated by demultiplexer 410 into 6 streams of pulses, each streamhaving a particular wavelength and a pulse repetition frequency ofapproximately 700 kHz.

FIG. 30 illustrates an example laser 300 where the laser 300 is coupledto multiple optical links (330-1, 330-2, . . . , 330-N) that eachinclude an amplifier (470-1, 470-2, . . . , 470-N). In particularembodiments, each optical link of a lidar system 100 may include a gainfiber 660 of a fiber-optic amplifier 470, where the gain fiber amplifiespulses while propagating from laser 300 to a corresponding sensor head310. In particular embodiments, laser 300 may include one or more laserdiodes 440, one or more multiplexers 412, one or more optical amplifiers470, and one or more demultiplexers 410. In the example of FIG. 30,optical pulses from N laser diodes (440-1, 440-2, . . . , 440-N) arecombined together by multiplexer 412, and the combined optical pulsesare amplified by amplifier 470. After amplification, demultiplexer 410distributes the amplified pulses between the N optical links (330-1,330-2, . . . , 330-N). Each of the N optical links includes a gain fiber660 of an amplifier 470, and the pulses are amplified as they propagatealong each optical link 330 to a corresponding sensor head 310.

In particular embodiments, a lidar system 100 may include one or moremultiplexers 412 or one or more demultiplexers 410 configured to combineor distribute optical pulses in any suitable manner. The multiplexers412 or demultiplexers 410 may be located at any suitable location withinthe lidar system 100. As an example, a demultiplexer 410 may be locatedafter one or more optical amplifiers 470 and may be configured todistribute amplified pulses among two or more optical links 330.Additionally, each of the optical links 330 may also include an opticalamplifier 470. As another example, a multiplexer 412 may be locatedbefore an optical amplifier 470 and may be configured to combine lightfrom multiple laser diodes 440. The laser diodes 440 may be coupleddirectly to the multiplexer 412, or the light from each laser diode 440may be amplified separately prior to being combined by the multiplexer412.

FIG. 31 illustrates an example laser 300 with multiple laser diodes(440-1, 440-2, . . . , 440-N) coupled to multiple respective opticallinks (330-1, 330-2, . . . , 330-N) that each include an amplifier(470-1, 470-2, . . . , 470-N). In particular embodiments, laser 300 mayinclude multiple laser diodes (440-1, 440-2, . . . , 440-N), where eachlaser diode is separately coupled to a corresponding optical link. Inthe example of FIG. 31, the N laser diodes (440-1, 440-2, . . . , 440-N)are individually coupled to N respective optical links (330-1, 330-2, .. . , 330-N), and each optical link includes an optical amplifier. Inparticular embodiments, laser 300 may also include N optical amplifiers470 (not illustrated in FIG. 31), where each amplifier is configured toamplify the pulses produced by a particular laser diode before thepulses are coupled to a corresponding optical link.

FIG. 32 illustrates an example lidar system 100 with an example overlapmirror 115. In particular embodiments, a lidar system 100 may include alight source 110 configured to emit pulses of light and a scanner 120configured to scan at least a portion of the emitted pulses of lightacross a field of regard. As an example, the optical pulses produced bylight source 110 may pass through aperture 752 of overlap mirror 115 andthen may be coupled to scanner 120. As another example, optical pulsesproduced by light source 110 may pass through a demultiplexer 410 (notillustrated in FIG. 32) which sends a portion of the pulses to scanner120. The portion of the pulses sent to scanner 120 may include afraction of the pulses emitted by light source 110 (e.g., 1 out of every6 pulses emitted by light source 110) or may include a fraction of eachpulse emitted by light source 110 (e.g., each pulse may be split into 6pulses, and one of the 6 split pulses may be sent to the scanner 120. Inparticular embodiments, a lidar system 100 may include a receiver 140configured to detect at least a portion of the scanned pulses of lightscattered by a target 130 located a distance from the lidar system 100.As an example, a pulse of light that is directed downrange from lidarsystem 100 by scanner 120 (e.g., as part of output beam 125) may scatteroff a target 130, and a portion of the scattered light may propagateback to the lidar system 100 (e.g., as part of input beam 135) and bedetected by receiver 140.

In particular embodiments, light source 110, scanner 120, and receiver140 may be packaged together within a single housing. As an example, alidar-system enclosure may contain a light source 110, overlap mirror115, scanner 120, and receiver 140 of a lidar system 100. Additionally,the lidar-system enclosure may include a controller 150, or a controller150 may be located remotely from the enclosure. The lidar-systemenclosure may also include one or more electrical connections forconveying electrical power or electrical signals to or from theenclosure. In particular embodiments, light source 110 may be locatedremotely from scanner 120 and receiver 140. As an example, scanner 120and receiver 140 may be part of a sensor head 310 located remotely fromlight source 110. The sensor head 310 may be coupled to the light source110 by an optical link 330 which conveys at least a portion of thepulses of light emitted by the light source 110 to the sensor head 310.In particular embodiments, a lidar system 100 may include multiplesensor heads 310, where each sensor head 310 includes a respectivescanner 120 and receiver 140. The light source 110 may be coupled toeach sensor head 310 by a respective optical link 330 which conveys arespective portion of the pulses of light emitted by the light source110 from the light source 110 to each sensor head 310.

In particular embodiments, light source 110 may include a seed laser 400configured to produce optical seed pulses and one or more opticalamplifiers 470 that amplify the optical seed pulses to produce thepulses of light emitted by the light source 110. The seed laser 400 mayinclude one or more laser diodes 440, such as for example, one or moreFabry-Perot laser diodes, DFB lasers, or DBR lasers. In particularembodiments, light source 110 may include a laser diode 440 without anyoptical-amplification stages located after the laser diode 440. As anexample, light source 110 may include a pulsed laser diode (e.g., apulsed Fabry-Perot laser diode, DFB laser, or DBR laser) that is coupledto a scanner 120 without the emitted pulses from the pulsed laser diodebeing amplified.

In particular embodiments, light source 110 may include an eye-safelaser. An eye-safe laser may refer to a laser with an emissionwavelength, average power, peak power, peak intensity, pulse energy,beam size, beam divergence, or exposure time such that emitted lightfrom the laser presents little or no possibility of causing damage to aperson's eyes. As an example, light source 110 may be classified as aClass 1 laser product (as specified by the 60825-1 standard of theInternational Electrotechnical Commission (IEC)) or a Class I laserproduct (as specified by Title 21, Section 1040.10 of the United StatesCode of Federal Regulations (CFR)) that is safe under all conditions ofnormal use. In particular embodiments, light source 110 may include aneye-safe laser (e.g., a Class 1 or a Class I laser) configured tooperate at any suitable wavelength between approximately 1400 nm andapproximately 2100 nm. As an example, light source 110 may include aneye-safe laser with an operating wavelength between approximately 1400nm and approximately 1600 nm. As another example, light source 110 mayinclude an eye-safe laser with an operating wavelength betweenapproximately 1530 nm and approximately 1560 nm.

In particular embodiments, scanner 120 may include one or more mirrors,where each mirror is mechanically driven by a galvanometer scanner, aresonant scanner, a MEMS device, a voice coil motor, or any suitablecombination thereof. A galvanometer scanner (which may be referred to asa galvanometer actuator) may include a galvanometer-based scanning motorwith a magnet and coil. When an electrical current is supplied to thecoil, a rotational force is applied to the magnet, which causes a mirrorattached to the galvanometer scanner to rotate. The electrical currentsupplied to the coil may be controlled to dynamically change theposition of the galvanometer mirror. A resonant scanner (which may bereferred to as a resonant actuator) may include a spring-like mechanismdriven by an actuator to produce a periodic oscillation at asubstantially fixed frequency (e.g., 1 kHz). A MEMS-based scanningdevice may include a mirror with a diameter between approximately 1 and10 mm, where the mirror is rotated using electromagnetic orelectrostatic actuation. A voice coil motor (which may be referred to asa voice coil actuator) may include a magnet and coil. When an electricalcurrent is supplied to the coil, a translational force is applied to themagnet, which causes a mirror attached to the magnet to move or rotate.

In particular embodiments, a scanner 120 may include any suitable numberof mirrors driven by any suitable number of mechanical actuators. As anexample, a scanner 120 may include a single mirror configured to scan anoutput beam 125 along a single direction (e.g., a scanner 120 may be aone-dimensional scanner that scans along a horizontal or verticaldirection). The mirror may be driven by one actuator (e.g., agalvanometer) or two actuators configured to drive the mirror in apush-pull configuration. As another example, a scanner 120 may include asingle mirror that scans an output beam 125 along two directions (e.g.,horizontal and vertical). The mirror may be driven by two actuators,where each actuator provides rotational motion along a particulardirection or about a particular axis. As another example, a scanner 120may include two mirrors, where one mirror scans an output beam 125 alonga horizontal direction and the other mirror scans the output beam 125along a vertical direction. In the example of FIG. 32, scanner 120includes two mirrors, mirror 750A and mirror 750B. Mirror 750A may scanoutput beam 125 along a substantially horizontal direction, and mirror750B may scan the output beam 125 along a substantially verticaldirection.

In particular embodiments, a scanner 120 may include two mirrors, whereeach mirror is driven by a corresponding galvanometer scanner. As anexample, scanner 120 may include a galvanometer actuator that scansmirror 750A along a first direction (e.g., horizontal), and scanner 120may include another galvanometer actuator that scans mirror 750B along asecond direction (e.g., vertical). In particular embodiments, a scanner120 may include two mirrors, where one mirror is driven by a resonantactuator and the other mirror is driven by a galvanometer actuator. Asan example, a resonant actuator may scan mirror 750A along a firstdirection, and a galvanometer actuator may scan mirror 750B along asecond direction. The first and second directions may be substantiallyorthogonal to one another. As an example, the first direction may besubstantially horizontal, and the second direction may be substantiallyvertical, or vice versa. In particular embodiments, a scanner 120 mayinclude one mirror driven by two actuators which are configured to scanthe mirror along two substantially orthogonal directions. As an example,one mirror may be driven along a substantially horizontal direction by aresonant actuator or a galvanometer actuator, and the mirror may also bedriven along a substantially vertical direction by a galvanometeractuator. As another example, a mirror may be driven along twosubstantially orthogonal directions by two resonant actuators.

In particular embodiments, a scanner 120 may include a mirror configuredto be scanned along one direction by two actuators arranged in apush-pull configuration. Driving a mirror in a push-pull configurationmay refer to a mirror that is driven in one direction by two actuators.The two actuators may be located at opposite ends or sides of themirror, and the actuators may be driven in a cooperative manner so thatwhen one actuator pushes on the mirror, the other actuator pulls on themirror, and vice versa. As an example, a mirror may be driven along ahorizontal or vertical direction by two voice coil actuators arranged ina push-pull configuration. In particular embodiments, a scanner 120 mayinclude one mirror configured to be scanned along two axes, where motionalong each axis is provided by two actuators arranged in a push-pullconfiguration. As an example, a mirror may be driven along a horizontaldirection by two resonant actuators arranged in a horizontal push-pullconfiguration, and the mirror may be driven along a vertical directionby another two resonant actuators arranged in a vertical push-pullconfiguration.

In particular embodiments, a scanner 120 may include two mirrors whichare driven synchronously so that the output beam 125 is directed alongany suitable scan pattern 200. As an example, a galvanometer actuatormay drive mirror 750A with a substantially linear back-and-forth motion(e.g., the galvanometer may be driven with a substantiallytriangle-shaped waveform) that causes output beam 125 to trace asubstantially horizontal back-and-forth pattern. Additionally, anothergalvanometer actuator may scan mirror 750B relatively slowly along asubstantially vertical direction. For example, the two galvanometers maybe synchronized so that for every 64 horizontal traces, the output beam125 makes a single trace along a vertical direction. As another example,a resonant actuator may drive mirror 750A along a substantiallyhorizontal direction, and a galvanometer actuator may scan mirror 750Brelatively slowly along a substantially vertical direction.

In particular embodiments, a scanner 120 may include one mirror drivenby two or more actuators, where the actuators are driven synchronouslyso that the output beam 125 is directed along a particular scan pattern200. As an example, one mirror may be driven synchronously along twosubstantially orthogonal directions so that the output beam 125 followsa scan pattern 200 that includes substantially straight lines. Inparticular embodiments, a scanner 120 may include two mirrors drivensynchronously so that the synchronously driven mirrors trace out a scanpattern 200 that includes substantially straight lines. As an example,the scan pattern 200 may include a series of substantially straightlines directed substantially horizontally, vertically, or along anyother suitable direction. The straight lines may be achieved by applyinga dynamically adjusted deflection along a vertical direction (e.g., witha galvanometer actuator) as an output beam 125 is scanned along asubstantially horizontal direction (e.g., with a galvanometer orresonant actuator). If a vertical deflection is not applied, the outputbeam 125 may trace out a curved path as it scans from side to side. Byapplying a vertical deflection as the mirror is scanned horizontally, ascan pattern 200 that includes substantially straight lines may beachieved. In particular embodiments, a vertical actuator may be used toapply both a dynamically adjusted vertical deflection as the output beam125 is scanned horizontally as well as a discrete vertical offsetbetween each horizontal scan (e.g., to step the output beam 125 to asubsequent row of a scan pattern 200).

In the example of FIG. 32, lidar system 100 produces an output beam 125and receives light from an input beam 135. The output beam 125, whichincludes at least a portion of the pulses of light emitted by lightsource 110, may be scanned across a field of regard. The input beam 135may include at least a portion of the scanned pulses of light which arescattered by one or more targets 130 and detected by receiver 140. Inparticular embodiments, output beam 125 and input beam 135 may besubstantially coaxial. The input and output beams being substantiallycoaxial may refer to the beams being at least partially overlapped orsharing a common propagation axis so that input beam 135 and output beam125 travel along substantially the same optical path (albeit in oppositedirections). As output beam 125 is scanned across a field of regard, theinput beam 135 may follow along with the output beam 125 so that thecoaxial relationship between the two beams is maintained.

In particular embodiments, a lidar system 100 may include an overlapmirror 115 configured to overlap the input beam 135 and output beam 125so that they are substantially coaxial. In FIG. 32, the overlap mirror115 includes a hole, slot, or aperture 752 which the output beam 125passes through and a reflecting surface 754 that reflects at least aportion of the input beam 135 toward the receiver 140. The overlapmirror 115 may be oriented so that input beam 135 and output beam 125are at least partially overlapped. In particular embodiments, input beam135 may pass through a lens 756 which focuses the beam onto an activeregion of the receiver 140 (e.g., the active region may have a diameterd). In particular embodiments, overlap mirror 115 may have a reflectingsurface 754 that is substantially flat or the reflecting surface 754 maybe curved (e.g., mirror 115 may be an off-axis parabolic mirrorconfigured to focus the input beam 135 onto an active region of thereceiver 140).

In particular embodiments, aperture 752 may have any suitable size ordiameter Φ₁, and input beam 135 may have any suitable size or diameterΦ₂, where Φ₂ is greater than Φ₁. As an example, aperture 752 may have adiameter Φ₁ of approximately 0.2 mm, 0.5 mm, 1 mm, 2 mm, 3 mm, 5 mm, or10 mm, and input beam 135 may have a diameter Φ₂ of approximately 2 mm,5 mm, 10 mm, 15 mm, 20 mm, 30 mm, 40 mm, or 50 mm. In particularembodiments, reflective surface 754 of overlap mirror 115 may reflectgreater than or equal to 70% of input beam 135 toward the receiver 140.As an example, if reflective surface 754 has a reflectivity R at anoperating wavelength of the light source 110, then the fraction of inputbeam 135 directed toward the receiver 140 may be expressed asR×[1−(Φ₁/Φ₂)²]. For example, if R is 95%, Φ₁ is 2 mm, and Φ₂ is 10 mm,then approximately 91% of input beam 135 may be directed toward thereceiver 140 by reflective surface 754.

FIG. 33 illustrates an example light-source field of view (FOV_(L)) andreceiver field of view (FOV_(R)) for a lidar system 100. The lightsource 110 may emit pulses of light as the FOV_(L) and FOV_(R) arescanned across a field of regard of the lidar system 100. In particularembodiments, a light-source field of view may refer to an angular coneilluminated by the light source 110 at a particular instant of time.Similarly, the receiver field of view may refer to an angular cone overwhich the receiver 140 may receive or detect light at a particularinstant of time, and any light outside the receiver field of view maynot be received or detected. As an example, as the light-source field ofview is scanned across a field of regard, a portion of a pulse of lightemitted by the light source 110 may be sent downrange from lidar system100, and the pulse of light may be sent in the direction that theFOV_(L) is pointing at the time the pulse is emitted. The pulse of lightmay scatter off a target 130, and the receiver 140 may receive anddetect a portion of the scattered light that is directed along orcontained within the FOV_(R).

In particular embodiments, scanner 120 may be configured to scan both alight-source field of view and a receiver field of view across a fieldof regard of the lidar system 100. Multiple pulses of light may beemitted and detected as the scanner 120 scans the FOV_(L) and FOV_(R)across the field of regard of the lidar system 100 while tracing out ascan pattern 200. In particular embodiments, the light-source field ofview and the receiver field of view may be scanned synchronously withrespect to one another, so that as the FOV_(L) is scanned across a scanpattern 200, the FOV_(R) follows substantially the same path at the samescanning speed. Additionally, the FOV_(L) and FOV_(R) may maintain thesame relative position to one another as they are scanned across thefield of regard. As an example, the FOV_(L) may be substantiallyoverlapped with or centered inside the FOV_(R) (as illustrated in FIG.33), and this relative positioning between FOV_(L) and FOV_(R) may bemaintained throughout a scan. As another example, the FOV_(R) may lagbehind the FOV_(L) by a particular, fixed amount throughout a scan(e.g., the FOV_(R) may be offset from the FOV_(L) in a directionopposite the scan direction).

In particular embodiments, the FOV_(L) may have an angular size orextent Θ_(L) that is substantially the same as or that corresponds tothe divergence of the output beam 125, and the FOV_(R) may have anangular size or extent Θ_(R) that corresponds to an angle over which thereceiver 140 may receive and detect light. In particular embodiments,the receiver field of view may be any suitable size relative to thelight-source field of view. As an example, the receiver field of viewmay be smaller than, substantially the same size as, or larger than theangular extent of the light-source field of view. In particularembodiments, the light-source field of view may have an angular extentof less than or equal to 50 milliradians, and the receiver field of viewmay have an angular extent of less than or equal to 50 milliradians. TheFOV_(L) may have any suitable angular extent Θ_(L), such as for example,approximately 0.1 mrad, 0.2 mrad, 0.5 mrad, 1 mrad, 1.5 mrad, 2 mrad, 3mrad, 5 mrad, 10 mrad, 20 mrad, 40 mrad, or 50 mrad. Similarly, theFOV_(R) may have any suitable angular extent Θ_(R), such as for example,approximately 0.1 mrad, 0.2 mrad, 0.5 mrad, 1 mrad, 1.5 mrad, 2 mrad, 3mrad, 5 mrad, 10 mrad, 20 mrad, 40 mrad, or 50 mrad. In particularembodiments, the light-source field of view and the receiver field ofview may have approximately equal angular extents. As an example, Θ_(L)and Θ_(R) may both be approximately equal to 1 mrad, 2 mrad, or 3 mrad.In particular embodiments, the receiver field of view may be larger thanthe light-source field of view, or the light-source field of view may belarger than the receiver field of view. As an example, Θ_(L) may beapproximately equal to 1.5 mrad, and Θ_(R) may be approximately equal to3 mrad.

In particular embodiments, a pixel 210 may represent or may correspondto a light-source field of view. As the output beam 125 propagates fromthe light source 110, the diameter of the output beam 125 (as well asthe size of the corresponding pixel 210) may increase according to thebeam divergence Θ_(L). As an example, if the output beam 125 has a Θ_(L)of 2 mrad, then at a distance of 100 m from the lidar system 100, theoutput beam 125 may have a size or diameter of approximately 20 cm, anda corresponding pixel 210 may also have a corresponding size or diameterof approximately 20 cm. At a distance of 200 m from the lidar system100, the output beam 125 and the corresponding pixel 210 may each have adiameter of approximately 40 cm.

FIG. 34 illustrates an example light-source field of view and receiverfield of view with a corresponding scan direction. In particularembodiments, scanner 120 may scan the FOV_(L) and FOV_(R) along anysuitable scan direction or combination of scan directions, such as forexample, left to right, right to left, upward, downward, or any suitablecombination thereof. As an example, the FOV_(L) and FOV_(R) may follow aleft-to-right scan direction (as illustrated in FIG. 34) across a fieldof regard, and then the FOV_(L) and FOV_(R) may travel back across thefield of regard in a right-to-left scan direction. In particularembodiments, a light-source field of view and a receiver field of viewmay be at least partially overlapped during scanning. As an example, theFOV_(L) and FOV_(R) may have any suitable amount of angular overlap,such as for example, approximately 1%, 2%, 5%, 10%, 25%, 50%, 75%, 90%,or 100% of angular overlap. As another example, if Θ_(L) and Θ_(R) are 2mrad, and FOV_(L) and FOV_(R) are offset from one another by 1 mrad,then FOV_(L) and FOV_(R) may be referred to as having a 50% angularoverlap. As another example, the FOV_(L) and FOV_(R) may besubstantially coincident with one another and may have an angularoverlap of approximately 100%. In the example of FIG. 34, the FOV_(L)and FOV_(R) are approximately the same size and have an angular overlapof approximately 90%.

FIG. 35 illustrates an example receiver field of view that is offsetfrom a light-source field of view. In particular embodiments, a FOV_(L)and FOV_(R) may be scanned along a particular scanning direction, andthe FOV_(R) may be offset from the FOV_(L) in a direction opposite thescanning direction. In the example of FIG. 35, the FOV_(L) and FOV_(R)are approximately the same size, and the FOV_(R) lags behind the FOV_(L)so that the FOV_(L) and FOV_(R) have an angular overlap of approximately5%. In particular embodiments, the FOV_(R) may be configured to lagbehind the FOV_(L) to produce any suitable angular overlap, such as forexample, an angular overlap of less than or equal to 50%, 25%, 5%, 1%,or 0.1%. After a pulse of light is emitted by light source 110, thepulse may scatter from a target 130, and some of the scattered light maypropagate back to the lidar system 100 along a path that corresponds tothe orientation of the light-source field of view at the time the pulsewas emitted. As the pulse of light propagates to and from the target130, the receiver field of view moves in the scan direction andincreases its overlap with the previous location of the light-sourcefield of view (e.g., the location of the light-source field of view whenthe pulse was emitted). For a close-range target (e.g., a target 130located within 20% of the maximum range of the lidar system), when thereceiver 140 detects scattered light from the emitted pulse, thereceiver field of view may overlap less than or equal to 20% of theprevious location of the light-source field of view. The receiver 140may receive less than or equal to 20% of the scattered light thatpropagates back to the lidar system 100 along the path that correspondsto the orientation of the light-source field of view at the time thepulse was emitted. However, since the target 130 is located relativelyclose to the lidar system 100, the receiver 140 may still receive asufficient amount of light to produce a signal indicating that a pulsehas been detected. For a midrange target (e.g., a target 130 locatedbetween 20% and 80% of the maximum range of the lidar system 100), whenthe receiver 140 detects the scattered light, the receiver field of viewmay overlap between 20% and 80% of the previous location of thelight-source field of view. For a target 130 located a distance greaterthan or equal to 80% of the maximum range of the lidar system 100, whenthe receiver 140 detects the scattered light, the receiver field of viewmay overlap greater than or equal to 80% of the previous location of thelight-source field of view. For a target 130 located at the maximumrange from the lidar system 100, when the receiver 140 detects thescattered light, the receiver field of view may be substantiallyoverlapped with the previous location of the light-source field of view,and the receiver 140 may receive substantially all of the scatteredlight that propagates back to the lidar system 100.

FIG. 36 illustrates an example forward-scan direction and reverse-scandirection for a light-source field of view and a receiver field of view.In particular embodiments, a lidar system 100 may be configured so thatthe FOV_(R) is larger than the FOV_(L), and the receiver andlight-source FOVs may be substantially coincident, overlapped, orcentered with respect to one another. As an example, the FOV_(R) mayhave a diameter or angular extent Θ_(R), that is approximately 1.5×, 2×,3×, 4×, 5×, or 10× larger than the diameter or angular extent Θ_(L) ofthe FOV_(L). In the example of FIG. 36, the diameter of the receiverfield of view is approximately 2 times larger than the diameter of thelight-source field of view, and the two FOVs are overlapped and centeredwith respect to one another. The receiver field of view being largerthan the light-source field of view may allow the receiver 140 toreceive scattered light from emitted pulses in both scan directions(forward scan or reverse scan). In the forward-scan directionillustrated in FIG. 36, scattered light may be received primarily by theleft side of the FOV_(R), and in the reverse-scan direction, scatteredlight may be received primarily by the right side of the FOV_(R). Forexample, as a pulse of light propagates to and from a target 130 duringa forward scan, the FOV_(R) scans to the right, and scattered light thatreturns to the lidar system 100 may be received primarily by the leftportion of the FOV_(R).

In particular embodiments, a lidar system 100 may perform a series offorward and reverse scans. As an example, a forward scan may include theFOV_(L) and the FOV_(R) being scanned horizontally from left to right,and a reverse scan may include the two fields of view being scanned fromright to left. As another example, a forward scan may include theFOV_(L) and the FOV_(R) being scanned along any suitable direction(e.g., along a 45-degree angle), and a reverse scan may include the twofields of view being scanned along a substantially opposite direction.In particular embodiments, the forward and reverse scans may trace pathsthat are adjacent to or displaced with respect to one another. As anexample, a reverse scan may follow a line in the field of regard that isdisplaced above, below, to the left of, or to the right of a previousforward scan. As another example, a reverse scan may scan a row in thefield of regard that is displaced below a previous forward scan, and thenext forward scan may be displaced below the reverse scan. The forwardand reverse scans may continue in an alternating manner with each scanbeing displaced with respect to the previous scan until a complete fieldof regard has been covered. Scans may be displaced with respect to oneanother by any suitable angular amount, such as for example, byapproximately 0.05°, 0.1°, 0.2°, 0.5°, 1°, or 2°.

FIG. 37 illustrates an example InGaAs avalanche photodiode (APD) 760. Inparticular embodiments, a receiver 140 may include one or more APDs 760configured to receive and detect light from an input beam 135. Inparticular embodiments, an APD 760 may be configured to detect a portionof pulses of light which are scattered by a target 130 located downrangefrom lidar system 100. As an example, an APD 760 may receive a portionof a pulse of light scattered by a target 130, and the APD 760 maygenerate an electrical-current signal corresponding to the receivedpulse of light.

In particular embodiments, an APD 760 may include doped or undopedlayers of any suitable semiconductor material, such as for example,silicon, germanium, InGaAs, InGaAsP, or indium phosphide (InP).Additionally, an APD 760 may include an upper electrode 762 and a lowerelectrode 772 for coupling the ADP 760 to an electrical circuit. As anexample, the APD 760 may be electrically coupled to a voltage sourcethat supplies a reverse-bias voltage V to the APD 760. Additionally, theAPD 760 may be electrically coupled to a transimpedance amplifier whichreceives electrical current generated by the APD 760 and produces anoutput voltage signal that corresponds to the received current. Theupper electrode 762 or lower electrode 772 may include any suitableelectrically conductive material, such as for example a metal (e.g.,gold, copper, silver, or aluminum), a transparent conductive oxide(e.g., indium tin oxide), a carbon-nanotube material, or polysilicon. Inparticular embodiments, the upper electrode 762 may be partiallytransparent or may have an opening to allow input light 135 to passthrough to the active region of the APD 760. In FIG. 37, the upperelectrode 762 may have a ring shape that at least partially surroundsthe active region of the APD, where the active region refers to an areaover which the APD 760 may receive and detect input light 135. Theactive region may have any suitable size or diameter d, such as forexample, a diameter of approximately 25 μm, 50 μm, 80 μm, 100 μm, 200μm, 500 μm, 1 mm, 2 mm, or 5 mm.

In particular embodiments, an APD 760 may include any suitablecombination of any suitable semiconductor layers having any suitabledoping (e.g., n-doped, p-doped, or intrinsic undoped material). In theexample of FIG. 37, the InGaAs APD 760 includes a p-doped InP layer 764,an InP avalanche layer 766, an absorption layer 768 with n-doped InGaAsor InGaAsP, and an n-doped InP substrate layer 770. In particularembodiments, an APD 760 may include separate absorption and avalanchelayers, or a single layer may act as both an absorption and avalancheregion. An InGaAs APD 760 may operate electrically as a PN diode or aPIN diode, and during operation, the APD 760 may be reverse biased witha positive voltage V applied to the lower electrode 772 with respect tothe upper electrode 762. The applied reverse-bias voltage V may have anysuitable value, such as for example approximately 5 V, 10 V, 20 V, 30 V,50 V, 75 V, 100 V, or 200 V.

In FIG. 37, photons of input light 135 may be absorbed primarily in theabsorption layer 768, resulting in the generation of electron-hole pairs(which may be referred to as photo-generated carriers). As an example,the absorption layer 768 may be configured to absorb photonscorresponding to the operating wavelength of the lidar system 100 (e.g.,any suitable wavelength between approximately 1400 nm and approximately1600 nm). In the avalanche layer 766, an avalanche-multiplicationprocess occurs where carriers (e.g., electrons or holes) generated inthe absorption layer 768 collide with the semiconductor lattice of theabsorption layer 768, and produce additional carriers through impactionization. This avalanche process can repeat numerous times so that onephoto-generated carrier may result in the generation of multiplecarriers. As an example, a single photon absorbed in the absorptionlayer 768 may lead to the generation of approximately 10, 50, 100, 200,500, 1000, 10,000, or any other suitable number of carriers through anavalanche-multiplication process. The carriers generated in an APD 760may produce an electrical current that is coupled to an electricalcircuit which may perform signal amplification, sampling, filtering,signal conditioning, analog-to-digital conversion, time-to-digitalconversion, pulse detection, threshold detection, rising-edge detection,or falling-edge detection.

In particular embodiments, the number of carriers generated from asingle photo-generated carrier may increase as the applied reverse biasV is increased. If the applied reverse bias V is increased above aparticular value referred to as the APD breakdown voltage, then a singlecarrier can trigger a self-sustaining avalanche process (e.g., theoutput of the APD 760 is saturated regardless of the input light level).In particular embodiments, an APD 760 that is operated at or above abreakdown voltage may be referred to as a single-photon avalanche diode(SPAD) and may be referred to as operating in a Geiger mode or aphoton-counting mode. An APD 760 operated below a breakdown voltage maybe referred to as a linear APD 760, and the output current generated bythe APD may be sent to an amplifier circuit (e.g., a transimpedanceamplifier). In particular embodiments, receiver 140 may include an APDconfigured to operate as a SPAD and a quenching circuit configured toreduce a reverse-bias voltage applied to the SPAD when an avalancheevent occurs in the SPAD. An APD 760 configured to operate as a SPAD maybe coupled to an electronic quenching circuit that reduces the appliedvoltage V below the breakdown voltage when an avalanche-detection eventoccurs. Reducing the applied voltage may halt the avalanche process, andthe applied reverse-bias voltage may then be re-set to await asubsequent avalanche event. Additionally, the APD 760 may be coupled toa circuit that generates an electrical output pulse or edge when anavalanche event occurs.

In particular embodiments, an APD 760 or an APD 760 and a transimpedanceamplifier may have a noise-equivalent power (NEP) that is less than orequal to 100 photons, 50 photons, 30 photons, 20 photons, or 10 photons.As an example, an InGaAs APD 760 may be operated as a SPAD and may havea NEP of less than or equal to 20 photons. As another example, an InGaAsAPD 760 may be coupled to a transimpedance amplifier that produces anoutput voltage signal with a NEP of less than or equal to 50 photons.The NEP of an APD 760 is a metric that quantifies the sensitivity of theAPD 760 in terms of a minimum signal (or a minimum number of photons)that the APD 760 can detect. In particular embodiments, the NEP maycorrespond to an optical power (or to a number of photons) that resultsin a signal-to-noise ratio of 1, or the NEP may represent a thresholdnumber of photons above which an optical signal may be detected. As anexample, if an APD 760 has a NEP of 20 photons, then an input beam 135with 20 photons may be detected with a signal-to-noise ratio ofapproximately 1 (e.g., the APD 760 may receive 20 photons from the inputbeam 135 and generate an electrical signal representing the input beam135 that has a signal-to-noise ratio of approximately 1). Similarly, aninput beam 135 with 100 photons may be detected with a signal-to-noiseratio of approximately 5. In particular embodiments, a lidar system 100with an APD 760 (or a combination of an APD 760 and transimpedanceamplifier) having a NEP of less than or equal to 100 photons, 50photons, 30 photons, 20 photons, or 10 photons may offer improveddetection sensitivity with respect to a conventional lidar system thatuses a PN or PIN photodiode. As an example, an InGaAs PIN photodiodeused in a conventional lidar system may have a NEP of approximately 10⁴to 10⁵ photons, and the noise level in a lidar system with an InGaAs PINphotodiode may be 10³ to 10⁴ times greater than the noise level in alidar system 100 with an InGaAs APD detector 760.

In particular embodiments, an optical filter 630 located in front ofreceiver 140 may be configured to transmit light at one or moreoperating wavelengths of the light source 110 and attenuate light atsurrounding wavelengths. As an example, an optical filter 630 may be afree-space spectral filter located in front of APD 760. The spectralfilter may transmit light at the operating wavelength of the lightsource 110 (e.g., between approximately 1530 nm and 1560 nm) and mayattenuate light outside that wavelength range. As an example, light withwavelengths of approximately 400-1530 nm or 1560-2000 nm may beattenuated by any suitable amount, such as for example, by at least 5dB, 10 dB, 20 dB, 30 dB, or 40 dB.

FIG. 38 illustrates an APD 760 coupled to an example pulse-detectioncircuit 780. In particular embodiments, a pulse-detection circuit 780may include circuitry that receives a signal from a detector (e.g., anelectrical current from APD 760) and performs current-to-voltageconversion, signal amplification, sampling, filtering, signalconditioning, analog-to-digital conversion, time-to-digital conversion,pulse detection, threshold detection, rising-edge detection, orfalling-edge detection. The pulse-detection circuit 780 may determinewhether an optical pulse has been received by an APD 760 or maydetermine a time associated with receipt of an optical pulse by APD 760.In particular embodiments, a pulse-detection circuit 780 may include atransimpedance amplifier (TIA) 782, a gain circuit 784, a comparator786, or a time-to-digital converter (TDC) 788. In particularembodiments, a pulse-detection circuit 780 may be included in a receiver140 or a controller 150, or parts of a pulse-detection circuit 780 maybe included in a receiver 140 and controller 150. As an example, a TIA782 and a voltage-gain circuit 784 may be part of a receiver 140, and acomparator 786 and a TDC 788 may be part of a controller 150 that iscoupled to the receiver 140.

In particular embodiments, a pulse-detection circuit 780 may include aTIA 782 configured to receive an electrical-current signal from an APD760 and produce a voltage signal that corresponds to the receivedelectrical-current signal. As an example, in response to a receivedoptical pulse, an APD 760 may produce a current pulse corresponding tothe optical pulse. A TIA 782 may receive the current pulse from the APD760 and produce a voltage pulse that corresponds to the received currentpulse. In particular embodiments, a TIA 782 may also act as anelectronic filter. As an example, a TIA 782 may be configured as alow-pass filter that removes or attenuates high-frequency electricalnoise by attenuating signals above a particular frequency (e.g., above 1MHz, 10 MHz, 20 MHz, 50 MHz, 100 MHz, 200 MHz, or any other suitablefrequency). In particular embodiments, a pulse-detection circuit 780 mayinclude a gain circuit 784 configured to amplify a voltage signal. As anexample, a gain circuit 784 may include one or morevoltage-amplification stages that amplify a voltage signal received froma TIA 782. For example, the gain circuit 784 may receive a voltage pulsefrom a TIA 782, and the gain circuit 784 may amplify the voltage pulseby any suitable amount, such as for example, by a gain of approximately3 dB, 10 dB, 20 dB, 30 dB, 40 dB, or 50 dB. Additionally, the gaincircuit 784 may also act as an electronic filter configured to remove orattenuate electrical noise.

In particular embodiments, a pulse-detection circuit 780 may include acomparator 786 configured to receive a voltage signal from TIA 782 orgain circuit 784 and produce an electrical-edge signal (e.g., a risingedge or a falling edge) when the received voltage signal rises above orfalls below a particular threshold voltage V_(T). As an example, when areceived voltage rises above V_(T), a comparator 786 may produce arising-edge digital-voltage signal (e.g., a signal that steps fromapproximately 0 V to approximately 2.5 V, 3.3 V, 5 V, or any othersuitable digital-high level). As another example, when a receivedvoltage falls below V_(T), a comparator 786 may produce a falling-edgedigital-voltage signal (e.g., a signal that steps down fromapproximately 2.5 V, 3.3 V, 5 V, or any other suitable digital-highlevel to approximately 0 V). The voltage signal received by thecomparator 786 may be received from a TIA 782 or gain circuit 784 andmay correspond to an electrical-current signal generated by an APD 760.As an example, the voltage signal received by the comparator 786 mayinclude a voltage pulse that corresponds to an electrical-current pulseproduced by the APD 760 in response to receiving an optical pulse. Thevoltage signal received by the comparator 786 may be an analog signal,and an electrical-edge signal produced by the comparator 786 may be adigital signal.

In particular embodiments, a pulse-detection circuit 780 may include atime-to-digital converter (TDC) 788 configured to receive anelectrical-edge signal from a comparator 786 and determine an intervalof time between emission of a pulse of light by the light source 110 andreceipt of the electrical-edge signal. The output of the TDC 788 may bea numerical value that corresponds to the time interval determined bythe TDC 788. In particular embodiments, a TDC 788 may have an internalcounter or clock with any suitable period, such as for example, 5 ps, 10ps, 15 ps, 20 ps, 30 ps, 50 ps, 100 ps, 0.5 ns, 1 ns, 2 ns, 5 ns, or 10ns. As an example, the TDC 788 may have an internal counter or clockwith a 20 ps period, and the TDC 788 may determine that an interval oftime between emission and receipt of a pulse is equal to 25,000 timeperiods, which corresponds to a time interval of approximately 0.5microseconds. The TDC 788 may send the numerical value “25000” to aprocessor or controller 150 of the lidar system 100. In particularembodiments, a lidar system 100 may include a processor configured todetermine a distance from the lidar system 100 to a target 130 based atleast in part on an interval of time determined by a TDC 788. As anexample, the processor may be an ASIC or FPGA and may be a part ofcontroller 150. The processor may receive a numerical value (e.g.,“25000”) from the TDC 788, and based on the received value, theprocessor may determine the distance from the lidar system 100 to atarget 130.

In particular embodiments, determining an interval of time betweenemission and receipt of a pulse of light may be based on determining (1)a time associated with the emission of the pulse by light source 110 orlidar system 100 and (2) a time when scattered light from the pulse isdetected by receiver 140. As an example, a TDC 788 may count the numberof time periods or clock cycles between an electrical edge associatedwith emission of a pulse of light and an electrical edge associated withdetection of scattered light from the pulse. Determining when scatteredlight from the pulse is detected by receiver 140 may be based ondetermining a time for a rising or falling edge (e.g., a rising orfalling edge produced by comparator 786) associated with the detectedpulse. In particular embodiments, determining a time associated withemission of a pulse of light may be based on an electrical triggersignal. As an example, light source 110 may produce an electricaltrigger signal for each pulse of light that is emitted, or an electricaldevice (e.g., function generator 420 or controller 150) may provide atrigger signal to the light source 110 to initiate the emission of eachpulse of light. A trigger signal associated with emission of a pulse maybe provided to TDC 788, and a rising edge or falling edge of the triggersignal may correspond to a time when a pulse is emitted. In particularembodiments, a time associated with emission of a pulse may bedetermined based on an optical trigger signal. As an example, a timeassociated with the emission of a pulse of light may be determined basedat least in part on detection of a portion of light from the emittedpulse of light. The portion of light may be detected by a separatedetector (e.g., a PIN photodiode or an APD 760) or by the receiver 140.A portion of light from an emitted pulse of light may be scattered orreflected from a surface (e.g., a surface of a beam splitter or asurface of light source 110, mirror 115, or scanner 120) located withinlidar system 100 or sensor head 310. Some of the scattered or reflectedlight may be received by an APD 760 of receiver 140, and apulse-detection circuit 780 coupled to the APD 760 may determine that apulse has been received. The time at which the pulse was received may beassociated with the emission time of the pulse. In particularembodiments, receiver 140 may include one APD 760 and onepulse-detection circuit 780 configured to detect a portion of an emittedpulse of light that is scattered or reflected from within the lidarsystem 100 as well a portion of the pulse of light that is subsequentlyscattered by a target 130. In particular embodiments, receiver 140 mayinclude two APDs 760 and two pulse-detection circuits 780. One APD 760and pulse-detection circuit 780 may detect a portion of an emitted pulseof light that is scattered or reflected from within the lidar system100, and the other APD 760 and pulse-detection circuit 780 may detect aportion of the pulse of light scattered by a target 130.

In particular embodiments, a lidar system 100 may include a processorconfigured to determine a distance D from the lidar system 100 to atarget 130 based at least in part on a round-trip time of flight for apulse of light emitted by the light source 110 to travel from the lidarsystem 100 to the target 130 and back to the lidar system 100. Inparticular embodiments, a round-trip time of flight for a pulse of lightmay be determined based at least in part on a rising edge or a fallingedge associated with the pulse of light detected by receiver 140. As anexample, a pulse of light detected by receiver 140 may generate acurrent pulse in an APD 760, which results in a rising-edge signalproduced by a comparator 786 coupled to the APD 760. In particularembodiments, a lidar system 100 may include a TDC 788 configured todetermine a time interval between emission of a pulse of light by lightsource 110 and detection by receiver 140 of at least a portion of thepulse of light scattered by a target 130.

FIG. 39 illustrates an APD 760 coupled to an example multi-channelpulse-detection circuit 780. In particular embodiments, a multi-channelpulse-detection circuit 780 may include two or more comparators 786 anda TDC 788 with two or more input channels. In the example of FIG. 39,the multi-channel pulse detection circuit includes a TIA 782 thatreceives a current signal from APD 760 and a gain circuit 784 thatboosts a voltage signal provided by TIA 782. The amplified voltagesignal from the gain circuit 784 is sent to the N comparators(comparators 786-1, 786-2, . . . , 786-N), and each comparator issupplied with a particular reference or threshold voltage (V_(T1),V_(T2), . . . , V_(T-N)). In particular embodiments, a multi-channelpulse-detection circuit 780 may include 2, 3, 4, 6, 8, 16, 32, 64, 128,or any other suitable number of comparators 786. As an example, amulti-channel pulse-detection circuit 780 may include N=8 comparators786, and each comparator may be configured to provide a rising orfalling edge to TDC 788 when a voltage signal provided by TIA 782 orgain circuit 784 rises above or falls below a particular thresholdvoltage V_(T). For example, four of the comparators 786 may provide arising edge when the voltage signal rises above 0.2 V, 0.4 V, 0.6 V, and0.8 V, respectively, and the other four comparators 786 may provide afalling edge when the voltage signal falls below 0.2 V, 0.4 V, 0.6 V,and 0.8 V, respectively. A multi-channel pulse-detection circuit 780 mayprovide additional information about a received pulse of light, such asfor example, a shape of the pulse, a duration of the pulse, or timinginformation about the rising edge, falling edge, or peak of the pulse.

In particular embodiments, a multi-channel pulse-detection circuit 780may include two comparators (786-1, 786-2). The first comparator 786-1may produce a first electrical-edge signal when a voltage signalprovided by TIA 782 or gain circuit 784 rises above a threshold voltageV_(T1). The second comparator 786-2 may produce a second electrical-edgesignal when the voltage signal falls below a threshold voltage V_(T2).The threshold voltages V_(T1) and V_(T2) may be the same or may bedifferent voltages. As an example, if V_(T1) and V_(T2) are the same,the edge from the first comparator 786-1 may correspond to a particularlevel of a rising edge of a received pulse, and the edge from the secondcomparator 786-2 may correspond to the same level of a falling edge ofthe received pulse. Additionally, the time difference between the twoedges may represent a width or duration of the pulse. In particularembodiments, a multi-channel pulse-detection circuit 780 may include aTDC 788 configured to receive the first and second electrical-edgesignals from comparators 786-1 and 786-2, respectively. The TDC 788 maydetermine a duration of the received pulse of light based on a timedifference between receipt of the first and second electrical-edgesignals. The TDC 788 may determine a first interval of time betweenemission of the pulse of light by the light source 110 and receipt ofthe first electrical-edge signal by the TDC 788. Additionally, the TDC788 may determine a second interval of time between emission of thepulse of light and receipt of the second electrical-edge signal. The TDC788 may determine a time associated with a peak of the received pulse oflight based at least in part on the first and second electrical-edgesignals (e.g., the peak may be located approximately midway between thetimes associated with the first and second electrical-edge signals). Inparticular embodiments, a processor or controller 150 may determine adistance from the lidar system 100 to a target 130 based at least inpart on a duration of a received pulse of light, a shape of a receivedpulse of light, a first or second interval of time associated with arising or falling edge, respectively, of a received pulse of light, or atime associated with a peak of a received pulse of light.

FIG. 40 illustrates an example receiver 140 that includes two APDs(760A, 760B) coupled to a logic circuit 792. In particular embodiments,a receiver 140 may include two or more APDs 760 which are coupled to alogic circuit 792 (e.g., each APD may be coupled to the logic circuitthrough a pulse-detection circuit). The logic circuit 792 may includeone or more logic gates (e.g., one or more AND gates), where the logicgates are configured to produce an output indicating that the receiver140 has detected an optical pulse only if each of the APDs (760A, 760B)or their associated pulse-detection circuits (780A, 780B) produces anelectrical signal corresponding to detection of the optical pulse. Inthe example of FIG. 40, input beam 135 is split by beam splitter 790into two beams which are coupled to APDs 760A and 760B. APD 760A iscoupled to pulse-detection circuit 780A, and APD 760B is coupled topulse-detection circuit 780B. Each pulse-detection circuit illustratedin FIG. 40 may include a TIA 782, a gain circuit 784, or a comparator786, and a comparator 786 of each pulse-detection circuit may provide adigital signal to the logic circuit 792. The logic circuit 792 in FIG.40 includes a single AND gate which may be configured to provide anelectrical-edge signal to TDC 788 only if both pulse-detection circuits780A and 780B provide a digital-high signal to the AND gate. Thereceiver 140 illustrated in FIG. 40 provides redundancy that may reducethe probability of false pulse-detection events caused by noise (e.g.,noise in an APD resulting from dark current or thermally induced carriergeneration). A noise event in APD 760A or 760B may cause an associatedpulse-detection circuit 780A or 780B to produce a digital-high signal.However, the AND gate will not send an electrical-edge signal to the TDC788 if it receives a digital-high signal from only one of thepulse-detection circuits 780A or 780B. The AND gate will only send anelectrical-edge signal to the TDC 788 if it receives a digital-highsignal from both pulse-detection circuits 780A and 780B, which indicatesthat both APDs 760A and 760B have detected an optical pulse.

FIG. 41 illustrates an example detector array 796. In particularembodiments, a receiver 140 may include an array 796 of two or more APDs760. A detector array 796 may include any suitable number or arrangementof APDs 760. As an example, a detector array 796 may include two APDs760 arranged side-by-side or one above the other. An arrangement of twoside-by-side APDs 760 may be used to scan alternate pixels 210 across afield of regard (e.g., APD 760C may detect light from odd-numberedpixels 210, and APD 760D may detect light from even-numbered pixels210). The detector array 796 in FIG. 41 includes six APDs (760C, 760D,760E, 760F, 760G, and 760H) arranged in a 2×3 configuration. A detectorarray 796 may allow a lidar system 100 to simultaneously scan multiplerows in a field of regard. As an example, detector 760C or 760D may scana particular row (e.g., row #1), detector 760E or 760F may scan anotherrow (e.g., row #17), and detector 760G or 760H may scan a different row(e.g., row #33). On a subsequent scan across the field of regard,detector 760C or 760D may scan row #2, detector 760E or 760F may scanrow #18, and detector 760G or 760H may scan row #34.

FIG. 42 illustrates an example computer system 800. In particularembodiments, one or more computer systems 800 may perform one or moresteps of one or more methods described or illustrated herein. Inparticular embodiments, one or more computer systems 800 may providefunctionality described or illustrated herein. In particularembodiments, software running on one or more computer systems 800 mayperform one or more steps of one or more methods described orillustrated herein or may provide functionality described or illustratedherein. Particular embodiments may include one or more portions of oneor more computer systems 800. In particular embodiments, a computersystem may be referred to as a computing device, a computing system, acomputer, a general-purpose computer, or a data-processing apparatus.Herein, reference to a computer system may encompass one or morecomputer systems, where appropriate.

Computer system 800 may take any suitable physical form. As an example,computer system 800 may be an embedded computer system, a system-on-chip(SOC), a single-board computer system (SBC), a desktop computer system,a laptop or notebook computer system, a mainframe, a mesh of computersystems, a server, a tablet computer system, or any suitable combinationof two or more of these. As another example, all or part of computersystem 800 may be combined with, coupled to, or integrated into avariety of devices, including, but not limited to, a camera, camcorder,personal digital assistant (PDA), mobile telephone, smartphone,electronic reading device (e.g., an e-reader), game console, smartwatch, clock, calculator, television monitor, flat-panel display,computer monitor, vehicle display (e.g., odometer display or dashboarddisplay), vehicle navigation system, lidar system, ADAS, autonomousvehicle, autonomous-vehicle driving system, cockpit control, camera viewdisplay (e.g., display of a rear-view camera in a vehicle), eyewear, orhead-mounted display. Where appropriate, computer system 800 may includeone or more computer systems 800; be unitary or distributed; spanmultiple locations; span multiple machines; span multiple data centers;or reside in a cloud, which may include one or more cloud components inone or more networks. Where appropriate, one or more computer systems800 may perform without substantial spatial or temporal limitation oneor more steps of one or more methods described or illustrated herein. Asan example, one or more computer systems 800 may perform in real time orin batch mode one or more steps of one or more methods described orillustrated herein. One or more computer systems 800 may perform atdifferent times or at different locations one or more steps of one ormore methods described or illustrated herein, where appropriate.

As illustrated in the example of FIG. 42, computer system 800 mayinclude a processor 810, memory 820, storage 830, an input/output (I/O)interface 840, a communication interface 850, or a bus 860. Computersystem 800 may include any suitable number of any suitable components inany suitable arrangement.

In particular embodiments, processor 810 may include hardware forexecuting instructions, such as those making up a computer program. Asan example, to execute instructions, processor 810 may retrieve (orfetch) the instructions from an internal register, an internal cache,memory 820, or storage 830; decode and execute them; and then write oneor more results to an internal register, an internal cache, memory 820,or storage 830. In particular embodiments, processor 810 may include oneor more internal caches for data, instructions, or addresses. Processor810 may include any suitable number of any suitable internal caches,where appropriate. As an example, processor 810 may include one or moreinstruction caches, one or more data caches, or one or more translationlookaside buffers (TLBs). Instructions in the instruction caches may becopies of instructions in memory 820 or storage 830, and the instructioncaches may speed up retrieval of those instructions by processor 810.Data in the data caches may be copies of data in memory 820 or storage830 for instructions executing at processor 810 to operate on; theresults of previous instructions executed at processor 810 for access bysubsequent instructions executing at processor 810 or for writing tomemory 820 or storage 830; or other suitable data. The data caches mayspeed up read or write operations by processor 810. The TLBs may speedup virtual-address translation for processor 810. In particularembodiments, processor 810 may include one or more internal registersfor data, instructions, or addresses. Processor 810 may include anysuitable number of any suitable internal registers, where appropriate.Where appropriate, processor 810 may include one or more arithmeticlogic units (ALUs); may be a multi-core processor; or may include one ormore processors 810.

In particular embodiments, memory 820 may include main memory forstoring instructions for processor 810 to execute or data for processor810 to operate on. As an example, computer system 800 may loadinstructions from storage 830 or another source (such as, for example,another computer system 800) to memory 820. Processor 810 may then loadthe instructions from memory 820 to an internal register or internalcache. To execute the instructions, processor 810 may retrieve theinstructions from the internal register or internal cache and decodethem. During or after execution of the instructions, processor 810 maywrite one or more results (which may be intermediate or final results)to the internal register or internal cache. Processor 810 may then writeone or more of those results to memory 820. One or more memory buses(which may each include an address bus and a data bus) may coupleprocessor 810 to memory 820. Bus 860 may include one or more memorybuses. In particular embodiments, one or more memory management units(MMUs) may reside between processor 810 and memory 820 and facilitateaccesses to memory 820 requested by processor 810. In particularembodiments, memory 820 may include random access memory (RAM). This RAMmay be volatile memory, where appropriate. Where appropriate, this RAMmay be dynamic RAM (DRAM) or static RAM (SRAM). Memory 820 may includeone or more memories 820, where appropriate.

In particular embodiments, storage 830 may include mass storage for dataor instructions. As an example, storage 830 may include a hard diskdrive (HDD), a floppy disk drive, flash memory, an optical disc, amagneto-optical disc, magnetic tape, or a Universal Serial Bus (USB)drive or a combination of two or more of these. Storage 830 may includeremovable or non-removable (or fixed) media, where appropriate. Storage830 may be internal or external to computer system 800, whereappropriate. In particular embodiments, storage 830 may be non-volatile,solid-state memory. In particular embodiments, storage 830 may includeread-only memory (ROM). Where appropriate, this ROM may be mask ROM(MROM), programmable ROM (PROM), erasable PROM (EPROM), electricallyerasable PROM (EEPROM), flash memory, or a combination of two or more ofthese. Storage 830 may include one or more storage control unitsfacilitating communication between processor 810 and storage 830, whereappropriate. Where appropriate, storage 830 may include one or morestorages 830.

In particular embodiments, I/O interface 840 may include hardware,software, or both, providing one or more interfaces for communicationbetween computer system 800 and one or more I/O devices. Computer system800 may include one or more of these I/O devices, where appropriate. Oneor more of these I/O devices may enable communication between a personand computer system 800. As an example, an I/O device may include akeyboard, keypad, microphone, monitor, mouse, printer, scanner, speaker,camera, stylus, tablet, touch screen, trackball, another suitable I/Odevice, or any suitable combination of two or more of these. An I/Odevice may include one or more sensors. Where appropriate, I/O interface840 may include one or more device or software drivers enablingprocessor 810 to drive one or more of these I/O devices. I/O interface840 may include one or more I/O interfaces 840, where appropriate.

In particular embodiments, communication interface 850 may includehardware, software, or both providing one or more interfaces forcommunication (such as, for example, packet-based communication) betweencomputer system 800 and one or more other computer systems 800 or one ormore networks. As an example, communication interface 850 may include anetwork interface controller (NIC) or network adapter for communicatingwith an Ethernet or other wire-based network or a wireless NIC (WNIC); awireless adapter for communicating with a wireless network, such as aWI-FI network; or an optical transmitter (e.g., a laser or alight-emitting diode) or an optical receiver (e.g., a photodetector) forcommunicating using fiber-optic communication or free-space opticalcommunication. Computer system 800 may communicate with an ad hocnetwork, a personal area network (PAN), an in-vehicle network (IVN), alocal area network (LAN), a wide area network (WAN), a metropolitan areanetwork (MAN), or one or more portions of the Internet or a combinationof two or more of these. One or more portions of one or more of thesenetworks may be wired or wireless. As an example, computer system 800may communicate with a wireless PAN (WPAN) (such as, for example, aBLUETOOTH WPAN), a WI-FI network, a Worldwide Interoperability forMicrowave Access (WiMAX) network, a cellular telephone network (such as,for example, a Global System for Mobile Communications (GSM) network),or other suitable wireless network or a combination of two or more ofthese. As another example, computer system 800 may communicate usingfiber-optic communication based on 100 Gigabit Ethernet (100 GbE), 10Gigabit Ethernet (10 GbE), or Synchronous Optical Networking (SONET).Computer system 800 may include any suitable communication interface 850for any of these networks, where appropriate. Communication interface850 may include one or more communication interfaces 850, whereappropriate.

In particular embodiments, bus 860 may include hardware, software, orboth coupling components of computer system 800 to each other. As anexample, bus 860 may include an Accelerated Graphics Port (AGP) or othergraphics bus, a controller area network (CAN) bus, an Enhanced IndustryStandard Architecture (EISA) bus, a front-side bus (FSB), aHYPERTRANSPORT (HT) interconnect, an Industry Standard Architecture(ISA) bus, an INFINIBAND interconnect, a low-pin-count (LPC) bus, amemory bus, a Micro Channel Architecture (MCA) bus, a PeripheralComponent Interconnect (PCI) bus, a PCI-Express (PCIe) bus, a serialadvanced technology attachment (SATA) bus, a Video Electronics StandardsAssociation local bus (VLB), or another suitable bus or a combination oftwo or more of these. Bus 860 may include one or more buses 860, whereappropriate.

In particular embodiments, various modules, circuits, systems, methods,or algorithm steps described in connection with the implementationsdisclosed herein may be implemented as electronic hardware, computersoftware, or any suitable combination of hardware and software. Inparticular embodiments, computer software (which may be referred to assoftware, computer-executable code, computer code, a computer program,computer instructions, or instructions) may be used to perform variousfunctions described or illustrated herein, and computer software may beconfigured to be executed by or to control the operation of computersystem 800. As an example, computer software may include instructionsconfigured to be executed by processor 810. In particular embodiments,owing to the interchangeability of hardware and software, the variousillustrative logical blocks, modules, circuits, or algorithm steps havebeen described generally in terms of functionality. Whether suchfunctionality is implemented in hardware, software, or a combination ofhardware and software may depend upon the particular application ordesign constraints imposed on the overall system.

The following paragraphs describe various specific embodiments of alidar system and a laser system:

A lidar system comprising: a light source configured to emit pulses oflight; a plurality of optical links, wherein each optical link couplesthe light source to a corresponding sensor head of a plurality of sensorheads, wherein the optical link is configured to convey at least aportion of the emitted pulses of light from the light source to thecorresponding sensor head; and the plurality of sensor heads, whereineach sensor head comprises: a scanner configured to scan pulses of lightacross a field of regard of the sensor head, wherein the scanned pulsesof light comprise the portion of the emitted pulses of light conveyedfrom the light source to the sensor head by the corresponding opticallink; and a receiver configured to detect at least a portion of thescanned pulses of light scattered or reflected by a target locateddownrange from the sensor head.

The lidar system, wherein: the target is at least partially containedwithin the field of regard of the sensor head and is located a distancefrom the sensor head that is less than or equal to a maximum range ofthe lidar system; and the sensor head further comprises a processorconfigured to determine the distance from the sensor head to the targetbased at least in part on a time of flight for a pulse of light totravel from the sensor head to the target and back to the sensor head.

The lidar system, wherein the lidar system is incorporated into avehicle wherein the sensor heads are positioned to provide a 360-degreeview of an environment around the vehicle.

The lidar system, wherein each optical link comprises a fiber-opticcable having a length greater than or equal to 1 meter.

The lidar system, further comprising a plurality of electrical linkscorresponding to the plurality of optical links, wherein each electricallink couples the light source to a respective sensor head of theplurality of sensor heads, wherein the electrical link is configured toconvey electrical power or one or more electrical signals between thelight source and the respective sensor head.

The lidar system, wherein the light source comprises: a seed laserconfigured to produce low-power optical pulses; and one or more opticalamplifiers configured to amplify the low-power optical pulses to producethe pulses of light emitted by the light source.

The lidar system, wherein the light source further comprises one or moreoptical filters, wherein each optical filter is configured to reduce anamount of amplified spontaneous emission light produced by one or moreof the optical amplifiers.

The lidar system, wherein the light source further comprises asupplemental light source combined with the seed laser, wherein lightfrom the supplemental light source is configured to prevent at least oneof the optical amplifiers from spontaneously emitting an optical pulseduring a time after amplification of a first low-power optical pulse andprior to receipt of a second low-power optical pulse.

The lidar system, wherein the light source comprises: a plurality oflaser diodes, wherein each laser diode is configured to produce light ata different operating wavelength; and an optical multiplexer configuredto combine the light produced by each laser diode into a single opticalfiber.

The lidar system, wherein the light source comprises awavelength-tunable laser configured to produce optical pulses at aplurality of wavelengths of light corresponding to the plurality ofsensor heads, wherein each wavelength produced by the wavelength-tunablelaser is conveyed to a corresponding sensor head.

The lidar system, wherein the light source comprises an opticalamplifier comprising one or more optical filters, wherein each opticalfilter is configured to reduce an amount of amplified spontaneousemission light produced by the optical amplifier.

The lidar system, wherein: the lidar system comprises N optical linkscoupled to N respective sensor heads; and the light source comprises a1×N optical demultiplexer configured to distribute the emitted pulses oflight between the N optical links.

The lidar system, wherein the optical demultiplexer comprises anoptical-power splitter, an optical switch, or a wavelengthdemultiplexer.

The lidar system, wherein distributing the emitted pulses of lightbetween the N optical links comprises: splitting each emitted pulse oflight into N pulses of light; and sending each pulse of the N pulses toa corresponding optical link for transmission to a corresponding sensorhead.

The lidar system, wherein: the pulses of light emitted by the lightsource comprise pulses having N different wavelengths; and distributingthe emitted pulses of light between the N optical links comprisessending each pulse having a particular wavelength to a correspondingoptical link for transmission to a corresponding sensor head.

The lidar system, wherein each optical link comprises a gain fiber of afiber-optic amplifier, wherein the gain fiber is configured to amplifythe portion of the emitted pulses of light while propagating from thelight source to the corresponding sensor head.

The lidar system, wherein each optical link comprises a gain fiber of anoptical amplifier, wherein the gain fiber is distributed along a lengthof the optical link and is configured to amplify the portion of theemitted pulses of light while the portion of the emitted pulses of lightis conveyed from the light source to the corresponding sensor head.

The lidar system, wherein each sensor head further comprises an opticalamplifier configured to: amplify the pulses of light conveyed to thesensor head by the optical link; and send the amplified pulses of lightto the scanner for scanning across the field of regard of the sensorhead.

The lidar system, wherein the optical amplifier is a free-spaceamplifier or a fiber-optic amplifier.

A laser system comprising: a seed laser configured to produce opticalseed pulses; a first fiber-optic amplifier configured to amplify theseed pulses by a first amplifier gain to produce a first-amplifieroutput that comprises amplified seed pulses and amplified spontaneousemission (ASE); a first optical filter configured to remove from thefirst-amplifier output an amount of the ASE; and a second fiber-opticamplifier configured to receive the amplified seed pulses from the firstoptical filter and amplify the received pulses by a second amplifiergain to produce output pulses, wherein the output pulses haveoutput-pulse characteristics comprising: a pulse repetition frequency ofless than or equal to 100 MHz; a pulse duration of less than or equal to20 nanoseconds; and a duty cycle of less than or equal to 1%.

The laser system, wherein the output-pulse characteristics furthercomprise: an operating wavelength of between approximately 1400 nm and2050 nm; a pulse energy of greater than or equal to 10 nanojoules; apeak power of greater than or equal to 1 watt; and an average power ofless than or equal to 50 watts, wherein the ASE comprises less than orequal to 25% of the average power.

The laser system, wherein: the optical seed pulses have an average powerof greater than or equal to 1 microwatt; the output pulses have anaverage power of greater than or equal to 1 milliwatt; and the firstamplifier gain and the second amplifier gain together correspond to anoverall optical power gain of greater than or equal to 40 dB.

The laser system, wherein the seed laser comprises a laser diodeconfigured to be electrically driven by a pulse generator to produce theoptical seed pulses.

The laser system, wherein the seed laser comprises: a laser diodeconfigured to produce continuous-wave (CW) light; and an opticalmodulator configured to receive the CW light and produce the opticalseed pulses from the received CW light.

The laser system, wherein the seed laser comprises: a laser diodeconfigured to produce optical pulses having a duration τ; and an opticalmodulator configured to: receive the optical pulses from the laserdiode; and selectively transmit a portion of each of the receivedoptical pulses to produce the optical seed pulses, wherein each opticalseed pulse has a duration less than τ.

The laser system, wherein the seed laser comprises: a plurality of laserdiodes, wherein each laser diode is configured to produce light at adifferent wavelength; and an optical multiplexer configured to combinethe light produced by each laser diode into a single optical fiber.

The laser system, further comprising a wavelength-dependent delay lineconfigured to receive input light comprising a plurality of operatingwavelengths of the laser system and produce time-delayed light, whereinthe time-delayed light comprises the light at the plurality of operatingwavelengths, wherein each wavelength of the plurality of operatingwavelengths has a particular time delay based on the wavelength.

The laser system, wherein the delay line comprises: a circulator; and aplurality of fiber Bragg gratings (FBGs) corresponding to the pluralityof operating wavelengths, wherein: the FBGs are arranged in series andseparated from one another by a particular length of optical fiber; andeach FBG is configured to reflect one wavelength of the operatingwavelengths.

The laser system, wherein the seed laser comprises a wavelength-tunablelaser configured to produce light at a plurality of wavelengths.

The laser system, wherein the seed laser comprises a mode-locked fiberlaser and a pulse picker configured to extract optical pulses producedby the mode-locked fiber laser.

The laser system, wherein the first optical filter is configured toremove greater than or equal to 80% of the ASE from the first-amplifieroutput.

The laser system, wherein the first optical filter comprises a spectralfilter configured to transmit light at one or more operating wavelengthsof the laser system and attenuate light away from the transmittedwavelengths by at least 20 dB.

The laser system, wherein the first optical filter comprises a temporalfilter comprising an optical switch or a semiconductor opticalamplifier, wherein the temporal filter is configured to be in atransmitting state when an amplified seed pulse is present and to be ina non-transmitting state otherwise, wherein when operating in thenon-transmitting state, the ASE is substantially prevented from beingtransmitted through the first optical filter.

The laser system, further comprising a second optical filter configuredto receive the output pulses from the second amplifier and reduce anamount of ASE produced by the second amplifier.

The laser system, further comprising an optical demultiplexer configuredto receive the output pulses from the second fiber-optic amplifier anddistribute the output pulses to a plurality of optical links of a lidarsystem, wherein the optical links are coupled to a respective pluralityof sensor heads of the lidar system.

The laser system, further comprising an output collimator configured toreceive the output pulses from the second fiber-optic amplifier andproduce a free-space optical beam comprising the output pulses.

The laser system, wherein: the first fiber-optic amplifier comprises adouble-pass amplifier comprising: a circulator; an erbium-doped orerbium/ytterbium-doped gain fiber comprising a first end and a secondend, wherein the first end is coupled to the circulator; and a fiberBragg grating (FBG) coupled to the second end of the gain fiber, whereinthe FBG is configured to reflect light corresponding to one or moreoperating wavelengths of the laser system and transmit or attenuatelight that is away from the reflected wavelengths; and the secondfiber-optic amplifier comprises a booster amplifier comprising adouble-clad gain fiber comprising erbium dopants or erbium and ytterbiumdopants.

The laser system, wherein: the first fiber-optic amplifier comprises afirst single-pass amplifier comprising a first gain fiber comprisingerbium dopants or erbium and ytterbium dopants; the second fiber-opticamplifier comprises a second single-pass amplifier comprising a secondgain fiber comprising erbium dopants or erbium and ytterbium dopants;and the laser system further comprises a third fiber-optic amplifier,wherein the third amplifier comprises a booster amplifier comprising adouble-clad gain fiber comprising erbium dopants or erbium and ytterbiumdopants.

The laser system, wherein: the first fiber-optic amplifier comprises adouble-pass amplifier comprising: a circulator; an erbium-doped orerbium/ytterbium-doped gain fiber comprising a first end and a secondend, wherein the first end is coupled to the circulator; and a fiberBragg grating (FBG) coupled to the second end of the gain fiber, whereinthe FBG is configured to reflect light corresponding to one or moreoperating wavelengths of the laser system and transmit or attenuatelight that is away from the reflected wavelengths; the secondfiber-optic amplifier comprises a single-pass amplifier comprisingerbium-doped or erbium/ytterbium-doped gain fiber; and the laser systemfurther comprises a third fiber-optic amplifier, wherein the thirdamplifier comprises a booster amplifier comprising a double-clad gainfiber comprising erbium dopants or erbium and ytterbium dopants.

The laser system, wherein the second fiber-optic amplifier comprises abooster amplifier comprising a double-clad gain fiber comprising erbiumdopants or erbium and ytterbium dopants.

The laser system, wherein the booster amplifier further comprises acladding mode stripper.

The laser system, wherein the seed laser, the first amplifier, the firstoptical filter, and the second amplifier are packaged together within asingle housing.

The laser system, wherein the laser system further comprises a thirdfiber-optic amplifier configured to receive the output pulses from thesecond amplifier and amplify the output pulses by a third amplifiergain, wherein the third amplifier comprises a booster amplifiercomprising a double-clad gain fiber comprising erbium dopants or erbiumand ytterbium dopants.

The laser system, wherein the laser system is part of a lidar systemcomprising a light source, an optical link, and a sensor head, wherein:the optical link couples the light source to the sensor head; the seedlaser is disposed in the light source; the first fiber-optic amplifieris disposed in the light source, the optical link, or the sensor head;and the second fiber-optic amplifier is disposed in the light source,the optical link, or the sensor head.

The laser system, wherein: the first and second amplifiers are disposedin the light source; and the laser system further comprises a thirdfiber-optic amplifier comprising a gain fiber distributed along a lengthof the optical link.

The laser system, wherein: the first amplifier is disposed in the lightsource; and the second amplifier comprises a gain fiber distributedalong a length of the optical link.

The laser system, wherein: the first and second amplifiers are disposedin the light source; and the laser system further comprises a thirdamplifier disposed in the sensor head, wherein the third amplifiercomprises a free-space amplifier or a fiber-optic amplifier.

The laser system, wherein: the first amplifier is disposed in the lightsource; the second amplifier comprises a gain fiber distributed along alength of the optical link; and the laser system further comprises athird amplifier disposed in the sensor head, wherein the third amplifiercomprises a free-space amplifier or a fiber-optic amplifier.

A lidar system comprising: a light source configured to emit pulses oflight; a scanner configured to scan at least a portion of the emittedpulses of light across a field of regard; and a receiver configured todetect at least a portion of the scanned pulses of light scattered by atarget located a distance from the lidar system.

The lidar system, further comprising a sensor head located remotely fromthe light source, wherein: the sensor head comprises the scanner and thereceiver; and the sensor head is coupled to the light source by anoptical link, wherein the optical link conveys the portion of theemitted pulses of light from the light source to the sensor head.

The lidar system, wherein the lidar system further comprises one or moreadditional sensor heads, wherein: each of the additional sensor headscomprises a respective scanner and receiver; and the light source iscoupled to each of the additional sensor heads by a respective opticallink which conveys a respective portion of the emitted pulses of lightfrom the light source to each of the additional sensor heads.

The lidar system, wherein the lidar system is incorporated into avehicle wherein the sensor head and one or more additional sensor headsof the lidar system are positioned to provide a greater than or equal to30-degree view of an environment around the vehicle.

The lidar system, wherein the lidar system has a maximum range ofgreater than or equal to 50 meters.

The lidar system, wherein the field of regard comprises: a horizontalfield of regard greater than or equal to 25 degrees; and a verticalfield of regard greater than or equal to 5 degrees.

The lidar system, wherein the lidar system has a horizontal resolutionof greater than or equal to 100 pixels and a vertical resolution ofgreater than or equal to 4 pixels.

The lidar system, wherein the lidar system is configured to generatepoint clouds at a rate between approximately 0.1 frames per second andapproximately 1,000 frames per second.

The lidar system of, wherein the light source comprises a pulsed laserdiode.

The lidar system, wherein the light source comprises: a seed laserconfigured to produce optical seed pulses; and one or more opticalamplifiers configured to amplify the optical seed pulses to produce thepulses of light emitted by the light source.

The lidar system, wherein the seed laser comprises adistributed-feedback (DFB) laser or a distributed-Bragg reflector (DBR)laser.

The lidar system, wherein the light source comprises a booster amplifiercomprising a double-clad gain fiber comprising erbium dopants or erbiumand ytterbium dopants.

The lidar system, wherein the light source comprises: a plurality oflaser diodes, wherein each laser diode is configured to produce light ata different operating wavelength; and an optical multiplexer configuredto combine the light produced by each laser diode into a single opticalfiber.

The lidar system, wherein the light source is an eye-safe laser with anoperating wavelength between approximately 1400 nm and approximately1600 nm.

The lidar system, wherein the pulses of light emitted by the lightsource have pulse characteristics comprising: an operating wavelengthbetween approximately 1400 nm and approximately 1600 nm; a pulserepetition frequency of less than or equal to 100 MHz; a pulse durationof less than or equal to 20 nanoseconds; and a duty cycle of less thanor equal to 1%.

The lidar system, wherein the pulse characteristics further comprise: apulse energy of greater than or equal to 10 nanojoules; a peak power ofgreater than or equal to 1 watt; and an average power of less than orequal to 50 watts.

The lidar system, wherein the light source comprises an optical filterconfigured to transmit light at one or more operating wavelengths of thelight source and attenuate light away from the transmitted wavelengthsby at least 10 dB.

The lidar system, wherein the light source comprises an optical filterconfigured to reduce an amount of amplified spontaneous emission lightproduced by one or more optical amplifiers of the light source.

The lidar system, wherein the light source comprises a diode-pumpedsolid-state (DPSS) laser.

The lidar system, wherein the scanner comprises one or more mirrors,wherein each mirror is mechanically driven by a galvanometer scanner, aresonant scanner, a microelectromechanical systems (MEMS) device, or avoice coil motor.

The lidar system, wherein the scanner comprises: a first mirror drivenby a first galvanometer scanner that scans the first mirror along afirst direction; and a second mirror driven by a second galvanometerscanner that scans the second mirror along a second directionsubstantially orthogonal to the first direction.

The lidar system, wherein the scanner comprises: a first mirror drivenby a resonant scanner that scans the first mirror along a firstdirection; and a second mirror driven by a galvanometer scanner thatscans the second mirror along a second direction substantiallyorthogonal to the first direction.

The lidar system, wherein the scanner comprises two mirrors drivensynchronously, wherein the synchronously driven mirrors trace out a scanpattern that comprises substantially straight lines.

The lidar system, wherein the scanner comprises a mirror driven by twoactuators configured to scan the mirror along two substantiallyorthogonal directions.

The lidar system, wherein the scanner comprises a mirror configured tobe scanned along two axes, wherein motion along each axis is provided bytwo actuators arranged in a push-pull configuration.

The lidar system, wherein: an output beam of the lidar system comprisesthe portion of the emitted pulses of light which are scanned across thefield of regard; an input beam of the lidar system comprises the portionof the scanned pulses of light detected by the receiver; and the inputand output beams are substantially coaxial.

The lidar system, further comprising an overlap mirror configured tooverlap the input and output beams so that they are substantiallycoaxial, wherein the overlap mirror comprises: a hole, slot, or aperturewhich the output beam passes through; and a reflecting surface thatreflects at least a portion of the input beam toward the receiver.

The lidar system, wherein: scanning the portion of the emitted pulses oflight across the field of regard comprises scanning a field of view ofthe light source across the field of regard; and the scanner is furtherconfigured to scan a field of view of the receiver across the field ofregard, wherein the light-source field of view and the receiver field ofview are scanned synchronously with respect to one another.

The lidar system, wherein the light-source field of view and thereceiver field of view are at least partially overlapped duringscanning.

The lidar system, wherein: the light-source field of view and thereceiver field of view are scanned along a scanning direction; and thereceiver field of view is offset from the light-source field of view ina direction opposite the scanning direction.

The lidar system, wherein an angular extent of the light-source field ofview is approximately equal to an angular extent of the receiver fieldof view.

The lidar system, wherein: the light-source field of view has an angularextent of less than or equal to 50 milliradians; and the receiver fieldof view has an angular extent of less than or equal to 50 milliradians.

The lidar system, wherein: the receiver comprises an avalanchephotodiode (APD); and detecting the portion of the scanned pulses oflight scattered by the target comprises: receiving, by the APD, a pulseof light of the portion of the scanned pulses of light scattered by thetarget; and generating, by the APD, an electrical-current signalcorresponding to the received pulse of light.

The lidar system, wherein the receiver further comprises atransimpedance amplifier configured to receive the electrical-currentsignal from the APD and produce a voltage signal that corresponds to thereceived electrical-current signal.

The lidar system, wherein the receiver further comprises a comparatorconfigured to produce an electrical-edge signal when a voltage signalcorresponding to the electrical-current signal generated by the APDrises above a predetermined threshold voltage.

The lidar system, further comprising a time-to-digital converter (TDC)configured to: receive the electrical-edge signal; and determine aninterval of time between emission of the pulse of light by the lightsource and receipt of the electrical-edge signal.

The lidar system, wherein determining the interval of time comprisesdetermining a time associated with the emission of the pulse of light bythe light source, wherein the time associated with the emission of thepulse of light is determined based at least in part on detection by thereceiver of a portion of light from the emitted pulse of light.

The lidar system, further comprising a processor configured to determinethe distance from the lidar system to the target based at least in parton the interval of time determined by the TDC.

The lidar system, wherein the receiver further comprises: a firstcomparator configured to produce a first electrical-edge signal when avoltage signal corresponding to the electrical-current signal generatedby the APD rises above a first predetermined threshold voltage; a secondcomparator configured to produce a second electrical-edge signal whenthe voltage signal falls below a second predetermined threshold voltage;and a time-to-digital converter (TDC) configured to: receive the firstand second electrical-edge signals; determine a first interval of timebetween emission of the pulse of light by the light source and receiptof the first electrical-edge signal; and determine a second interval oftime between emission of the pulse of light by the light source andreceipt of the second electrical-edge signal.

The lidar system, further comprising a processor configured to determinethe distance from the lidar system to the target based at least in parton the first and second intervals of time.

The lidar system, further comprising an optical filter located in frontof the receiver, wherein the optical filter is configured to transmitlight at one or more operating wavelengths of the light source andattenuate light at surrounding wavelengths by at least 10 dB.

The lidar system, wherein the receiver comprises an array of two or moreavalanche photodiodes (APDs).

The lidar system, wherein the receiver comprises: an avalanchephotodiode (APD) configured to operate as a single-photon avalanchediode (SPAD); and a quenching circuit configured to reduce areverse-bias voltage applied to the SPAD when an avalanche event occursin the SPAD.

The lidar system, wherein the receiver comprises: two or more avalanchephotodiodes (APDs); and one or more logic gates coupled to the APDs,wherein the logic gates are configured to produce an output indicatingthat the receiver has detected an optical pulse only if each of the APDsproduces an electrical signal corresponding to detection of the opticalpulse.

The lidar system, further comprising a processor configured to determinethe distance from the lidar system to the target based at least in parton a round-trip time of flight for a pulse of light emitted by the lightsource to travel from the lidar system to the target and back to thelidar system.

The lidar system, wherein the round-trip time of flight is determinedbased at least in part on a rising edge or a falling edge associatedwith the pulse of light detected by the receiver.

The lidar system, further comprising a time-to-digital converter (TDC)configured to determine a time interval between emission of a pulse oflight by the light source and detection by the receiver of at least aportion of the pulse of light scattered by the target.

In particular embodiments, a computing device may be used to implementvarious modules, circuits, systems, methods, or algorithm stepsdisclosed herein. As an example, all or part of a module, circuit,system, method, or algorithm disclosed herein may be implemented orperformed by a general-purpose single- or multi-chip processor, adigital signal processor (DSP), an ASIC, a FPGA, any other suitableprogrammable-logic device, discrete gate or transistor logic, discretehardware components, or any suitable combination thereof. Ageneral-purpose processor may be a microprocessor, or, any conventionalprocessor, controller, microcontroller, or state machine. A processormay also be implemented as a combination of computing devices, e.g., acombination of a DSP and a microprocessor, a plurality ofmicroprocessors, one or more microprocessors in conjunction with a DSPcore, or any other such configuration.

In particular embodiments, one or more implementations of the subjectmatter described herein may be implemented as one or more computerprograms (e.g., one or more modules of computer-program instructionsencoded or stored on a computer-readable non-transitory storage medium).As an example, the steps of a method or algorithm disclosed herein maybe implemented in a processor-executable software module which mayreside on a computer-readable non-transitory storage medium. Inparticular embodiments, a computer-readable non-transitory storagemedium may include any suitable storage medium that may be used to storeor transfer computer software and that may be accessed by a computersystem. Herein, a computer-readable non-transitory storage medium ormedia may include one or more semiconductor-based or other integratedcircuits (ICs) (such, as for example, field-programmable gate arrays(FPGAs) or application-specific ICs (ASICs)), hard disk drives (HDDs),hybrid hard drives (HHDs), optical discs (e.g., compact discs (CDs),CD-ROM, digital versatile discs (DVDs), blue-ray discs, or laser discs),optical disc drives (ODDs), magneto-optical discs, magneto-opticaldrives, floppy diskettes, floppy disk drives (FDDs), magnetic tapes,flash memories, solid-state drives (SSDs), RAM, RAM-drives, ROM, SECUREDIGITAL cards or drives, any other suitable computer-readablenon-transitory storage media, or any suitable combination of two or moreof these, where appropriate. A computer-readable non-transitory storagemedium may be volatile, non-volatile, or a combination of volatile andnon-volatile, where appropriate.

In particular embodiments, certain features described herein in thecontext of separate implementations may also be combined and implementedin a single implementation. Conversely, various features that aredescribed in the context of a single implementation may also beimplemented in multiple implementations separately or in any suitablesub-combination. Moreover, although features may be described above asacting in certain combinations and even initially claimed as such, oneor more features from a claimed combination may in some cases be excisedfrom the combination, and the claimed combination may be directed to asub-combination or variation of a sub-combination.

While operations may be depicted in the drawings as occurring in aparticular order, this should not be understood as requiring that suchoperations be performed in the particular order shown or in sequentialorder, or that all operations be performed. Further, the drawings mayschematically depict one more example processes or methods in the formof a flow diagram or a sequence diagram. However, other operations thatare not depicted may be incorporated in the example processes or methodsthat are schematically illustrated. For example, one or more additionaloperations may be performed before, after, simultaneously with, orbetween any of the illustrated operations. Moreover, one or moreoperations depicted in a diagram may be repeated, where appropriate.Additionally, operations depicted in a diagram may be performed in anysuitable order. Furthermore, although particular components, devices, orsystems are described herein as carrying out particular operations, anysuitable combination of any suitable components, devices, or systems maybe used to carry out any suitable operation or combination ofoperations. In certain circumstances, multitasking or parallelprocessing operations may be performed. Moreover, the separation ofvarious system components in the implementations described herein shouldnot be understood as requiring such separation in all implementations,and it should be understood that the described program components andsystems may be integrated together in a single software product orpackaged into multiple software products.

Various embodiments have been described in connection with theaccompanying drawings. However, it should be understood that the figuresmay not necessarily be drawn to scale. As an example, distances orangles depicted in the figures are illustrative and may not necessarilybear an exact relationship to actual dimensions or layout of the devicesillustrated.

The scope of this disclosure encompasses all changes, substitutions,variations, alterations, and modifications to the example embodimentsdescribed or illustrated herein that a person having ordinary skill inthe art would comprehend. The scope of this disclosure is not limited tothe example embodiments described or illustrated herein. Moreover,although this disclosure describes or illustrates respective embodimentsherein as including particular components, elements, functions,operations, or steps, any of these embodiments may include anycombination or permutation of any of the components, elements,functions, operations, or steps described or illustrated anywhere hereinthat a person having ordinary skill in the art would comprehend.

The term “or” as used herein is to be interpreted as an inclusive ormeaning any one or any combination, unless expressly indicated otherwiseor indicated otherwise by context. Therefore, herein, the expression “Aor B” means “A, B, or both A and B.” As another example, herein, “A, Bor C” means at least one of the following: A; B; C; A and B; A and C; Band C; A, B and C. An exception to this definition will occur if acombination of elements, devices, steps, or operations is in some wayinherently mutually exclusive.

As used herein, words of approximation such as, without limitation,“approximately, “substantially,” or “about” refer to a condition thatwhen so modified is understood to not necessarily be absolute or perfectbut would be considered close enough to those of ordinary skill in theart to warrant designating the condition as being present. The extent towhich the description may vary will depend on how great a change can beinstituted and still have one of ordinary skill in the art recognize themodified feature as having the required characteristics or capabilitiesof the unmodified feature. In general, but subject to the precedingdiscussion, a numerical value herein that is modified by a word ofapproximation such as “approximately” may vary from the stated value by±0.5%, ±1%, ±2%, ±3%, ±4%, ±5%, ±10%, ±12%, or ±15%.

As used herein, the terms “first,” “second,” “third,” etc. may be usedas labels for nouns that they precede, and these terms may notnecessarily imply a particular ordering (e.g., a particular spatial,temporal, or logical ordering). As an example, a system may be describedas determining a “first result” and a “second result,” and the terms“first” and “second” may not necessarily imply that the first result isdetermined before the second result.

As used herein, the terms “based on” and “based at least in part on” maybe used to describe or present one or more factors that affect adetermination, and these terms may not exclude additional factors thatmay affect a determination. A determination may be based solely on thosefactors which are presented or may be based at least in part on thosefactors. The phrase “determine A based on B” indicates that B is afactor that affects the determination of A. In some instances, otherfactors may also contribute to the determination of A. In otherinstances, A may be determined based solely on B.

What is claimed is:
 1. A lidar system comprising: a light sourceconfigured to emit a pulse of light into a field of view; a receiverconfigured to detect a return pulse of light which comprises at least aportion of the emitted pulse of light which is reflected or scattered bya target in the field of view, the receiver comprising: an avalanchephotodiode configured to generate an electrical-current pulsecorresponding to the return pulse of light, a transimpedance amplifierconfigured to produce a voltage pulse that corresponds to theelectrical-current pulse, a voltage amplifier configured to amplify thevoltage pulse to produce an amplified voltage pulse, a first comparatorconfigured to produce a first edge signal when the amplified voltagepulse exceeds a first threshold, and a time-to-digital converterconfigured to determine a first time interval based on an emission timeof the pulse of light and based on the first edge signal wherein theemission time of the pulse of light is determined from an opticaltrigger signal associated with detection by the receiver of a portion ofthe emitted pulse of light which is scattered or reflected from asurface located within the lidar system; and a processor configured todetermine a distance to the target using the first time interval.
 2. Thelidar system of claim 1, further comprising a sensor head locatedremotely from the light source, wherein: the sensor head comprises thereceiver; and the sensor head is coupled to the light source by anoptical link.
 3. The lidar system of claim 2, wherein the lidar systemfurther comprises one or more additional sensor heads, wherein: each ofthe additional sensor heads comprises a respective receiver; and thelight source is coupled to each of the additional sensor heads by arespective optical link.
 4. The lidar system of claim 3, wherein thelidar system is incorporated into a vehicle, and wherein the sensor headand the one or more additional sensor heads of the lidar system arepositioned about the vehicle to provide at least a 180-degree view of anenvironment around the vehicle.
 5. The lidar system of claim 1, whereinthe lidar system has a horizontal resolution of at least 100 pixels anda vertical resolution of at least 4 pixels.
 6. The lidar system of claim1, wherein the lidar system is configured to generate point clouds ofdistance measurements at a rate between 0.1 frames per second and 1,000frames per second.
 7. The lidar system of claim 1, wherein: the lightsource emits the pulse into a light source field of view; the receiverdetects the return pulse from a receiver field of view; the light-sourcefield of view and the receiver field of view are scanned along ascanning direction; and the receiver field of view is offset from thelight-source field of view in a direction opposite the scanningdirection.
 8. The lidar system of claim 1, wherein: the light sourceemits the pulse into a light source field of view; the receiver detectsthe return pulse from a receiver field of view; and an angular extent ofthe light source field of view is equal to an angular extent of thereceiver field of view.
 9. The lidar system of claim 1, wherein: thelight source emits the pulse into a light source field of view; thereceiver detects the return pulse from a receiver field of view; thelight-source field of view has an angular extent of less than or equalto 50 milliradians; and the receiver field of view has an angular extentof less than or equal to 50 milliradians.
 10. The lidar system of claim1, wherein the receiver further comprises: a second comparatorconfigured to produce a second edge signal when the amplified voltagepulse falls below a second threshold, wherein the time-to-digitalconverter is configured to determine a second time interval based on theemission time of the pulse of light by the light source and based on thesecond edge signal.
 11. The lidar system of claim 10, further comprisinga processor configured to determine the distance to the target based atleast in part on the first and second time intervals.
 12. The lidarsystem of claim 1, further comprising an optical filter, wherein theoptical filter is configured to transmit the return pulse and attenuateother light by at least 10 dB.
 13. The lidar system of claim 1, whereinthe receiver comprises an array of two or more avalanche photodiodes.14. The lidar system of claim 1, wherein the receiver comprises: anavalanche photodiode configured to operate as a single-photon avalanchediode (SPAD); and a quenching circuit configured to reduce areverse-bias voltage applied to the SPAD when an avalanche event occursin the SPAD.
 15. The lidar system of claim 1, wherein the receivercomprises: two or more avalanche photodiodes (APDs); and one or morelogic gates coupled to the APDs, wherein the logic gates are configuredto produce an output indicating that the receiver has detected thereturn pulse only if each of the APDs produces an electrical signalcorresponding to detection of the return pulse.
 16. The lidar system ofclaim 1, wherein the processor is configured to determine the distanceto the target based at least in part on a round-trip time of flight forthe pulse of light emitted by the light source to travel from the lidarsystem to the target and back to the lidar system.
 17. The lidar systemof claim 16, wherein the round-trip time of flight is determined basedat least in part on a rising edge or a falling edge associated with thereturn pulse of light detected by the receiver.
 18. The lidar system ofclaim 1, further comprising a plurality of comparators, the plurality ofcomparators being configured to determine when the amplified voltagepulse reaches a respective plurality of different reference values so asto provide information about the shape of the amplified voltage pulse.